diff --git a/backend/internal/service/merchant_member.go b/backend/internal/service/merchant_member.go
index 3b4afa3..2d44123 100644
--- a/backend/internal/service/merchant_member.go
+++ b/backend/internal/service/merchant_member.go
@@ -179,6 +179,8 @@ func (s *MerchantService) AddMember(merchantID uint, in AddMemberInput, actorUse
 		}
 		var user model.User
 		createdUser := false
+		reactivated := false
+		previousDefault := false
 		if in.UserID != 0 {
 			if err := tx.Where("id = ? AND status = ?", in.UserID, 1).First(&user).Error; err != nil {
 				return errors.New("用户不存在或已禁用")
@@ -195,29 +197,56 @@ func (s *MerchantService) AddMember(merchantID uint, in AddMemberInput, actorUse
 			if err != nil {
 				return err
 			}
-			user = model.User{Username: username, PasswordHash: string(hash), Nickname: fallbackName(in.Nickname, username), Role: model.RoleMerchant, Status: 1}
-			if err := tx.Create(&user).Error; err != nil {
-				return errors.New("员工用户名已存在")
+			err = tx.Where("username = ?", username).First(&user).Error
+			switch {
+			case err == nil:
+				existingMember, reuseErr := reusableDisabledMember(tx, merchantID, &user)
+				if reuseErr != nil {
+					return reuseErr
+				}
+				previousDefault = existingMember.IsDefault
+				updates := map[string]interface{}{
+					"password_hash": string(hash),
+					"role":          model.RoleMerchant,
+				}
+				if nickname := strings.TrimSpace(in.Nickname); nickname != "" {
+					updates["nickname"] = nickname
+				}
+				if err := tx.Model(&user).Updates(updates).Error; err != nil {
+					return err
+				}
+				reactivated = true
+			case errors.Is(err, gorm.ErrRecordNotFound):
+				user = model.User{Username: username, PasswordHash: string(hash), Nickname: fallbackName(in.Nickname, username), Role: model.RoleMerchant, Status: 1}
+				if err := tx.Create(&user).Error; err != nil {
+					return errors.New("员工用户名已存在")
+				}
+				createdUser = true
+			default:
+				return err
 			}
-			createdUser = true
 		}
 		if _, err := (&TenantService{db: tx}).MerchantRolePermissions(merchantID, in.Role); err != nil {
 			return err
 		}
 		member.UserID = user.ID
-		// 新建员工仅属于当前商户，登录时应直接进入该商户。
-		member.IsDefault = in.IsDefault || createdUser
+		// 新建或重新启用员工时，确保登录后进入当前商户。
+		member.IsDefault = in.IsDefault || createdUser || previousDefault
 		if err := tx.Clauses(clause.OnConflict{
 			Columns: []clause.Column{{Name: "merchant_id"}, {Name: "user_id"}},
 			DoUpdates: clause.Assignments(map[string]interface{}{
 				"role":       in.Role,
 				"status":     1,
-				"is_default": in.IsDefault,
+				"is_default": member.IsDefault,
 			}),
 		}).Create(member).Error; err != nil {
 			return err
 		}
-		return writeAudit(tx, &merchantID, &actorUserID, nil, "merchant.member.upsert", "merchant_member", fmt.Sprintf("%d:%d", merchantID, user.ID), map[string]string{"role": in.Role})
+		metadata := map[string]string{"role": in.Role}
+		if reactivated {
+			metadata["reactivated"] = "true"
+		}
+		return writeAudit(tx, &merchantID, &actorUserID, nil, "merchant.member.upsert", "merchant_member", fmt.Sprintf("%d:%d", merchantID, user.ID), metadata)
 	})
 	if err != nil {
 		return nil, err
@@ -228,6 +257,26 @@ func (s *MerchantService) AddMember(merchantID uint, in AddMemberInput, actorUse
 	return member, nil
 }
 
+// reusableDisabledMember 返回当前商户下可被“添加员工”重新启用的成员关系。
+// 仅允许本商户找回自己停用的普通员工；启用中的成员、负责人和其他商户的账号
+// 仍然保持用户名占用，避免通过重建账号接管他人身份。
+func reusableDisabledMember(tx *gorm.DB, merchantID uint, user *model.User) (*model.MerchantMember, error) {
+	if user.Role != model.RoleMerchant || user.Status != 1 {
+		return nil, errors.New("员工用户名已存在")
+	}
+	var member model.MerchantMember
+	if err := tx.Where("merchant_id = ? AND user_id = ?", merchantID, user.ID).First(&member).Error; err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return nil, errors.New("员工用户名已存在")
+		}
+		return nil, err
+	}
+	if member.Role == model.MemberRoleOwner || member.Status == 1 {
+		return nil, errors.New("员工用户名已存在")
+	}
+	return &member, nil
+}
+
 func (s *MerchantService) ListMembers(merchantID uint) ([]model.MerchantMember, error) {
 	var members []model.MerchantMember
 	if err := s.db.Preload("User").Where("merchant_id = ?", merchantID).Order("id ASC").Find(&members).Error; err != nil {
diff --git a/backend/internal/service/merchant_member_security_test.go b/backend/internal/service/merchant_member_security_test.go
index cb0c23f..d2ab57b 100644
--- a/backend/internal/service/merchant_member_security_test.go
+++ b/backend/internal/service/merchant_member_security_test.go
@@ -1,6 +1,7 @@
 package service
 
 import (
+	"strings"
 	"testing"
 	"time"
 
@@ -351,3 +352,123 @@ func TestUpdateMemberCanChangeNickname(t *testing.T) {
 		t.Fatalf("nickname should be kept, got %q", user.Nickname)
 	}
 }
+
+func TestAddMemberReactivatesDisabledMemberWithSameUsername(t *testing.T) {
+	db := newServiceTestDB(t)
+	svc := NewMerchantService(db, nil, NewTenantService(db))
+	merchantID, ownerUserID := seedMerchantWithOwner(t, db, "reuse-merchant", "reuse-owner", 1)
+	seedOperatorRole(t, db, merchantID)
+
+	oldHash, err := bcrypt.GenerateFromPassword([]byte("oldpass123"), bcrypt.DefaultCost)
+	if err != nil {
+		t.Fatalf("hash old password: %v", err)
+	}
+	staff := model.User{
+		Username: "kf_10", PasswordHash: string(oldHash), Nickname: "旧姓名",
+		Role: model.RoleMerchant, Status: 1, Phone: "13800001234",
+	}
+	if err := db.Create(&staff).Error; err != nil {
+		t.Fatalf("create staff: %v", err)
+	}
+	member := model.MerchantMember{
+		MerchantID: merchantID, UserID: staff.ID, Role: "support", Status: 1, IsDefault: true,
+	}
+	if err := db.Create(&member).Error; err != nil {
+		t.Fatalf("create member: %v", err)
+	}
+	if err := db.Model(&member).Update("status", 0).Error; err != nil {
+		t.Fatalf("disable member: %v", err)
+	}
+	member.Status = 0
+
+	created, err := svc.AddMember(merchantID, AddMemberInput{
+		Username: "kf_10", Password: "yaochao11", Nickname: "测试2", Role: model.MemberRoleOperator,
+	}, ownerUserID)
+	if err != nil {
+		t.Fatalf("re-add disabled member: %v", err)
+	}
+	if created.UserID != staff.ID {
+		t.Fatalf("reused user id = %d, want %d", created.UserID, staff.ID)
+	}
+	if created.Status != 1 || created.Role != model.MemberRoleOperator || !created.IsDefault {
+		t.Fatalf("unexpected reactivated member: %+v", created)
+	}
+	if created.User == nil || created.User.Username != "kf_10" || created.User.Nickname != "测试2" {
+		t.Fatalf("unexpected reactivated user: %+v", created.User)
+	}
+	var reloaded model.User
+	if err := db.First(&reloaded, staff.ID).Error; err != nil {
+		t.Fatalf("reload staff: %v", err)
+	}
+	if err := bcrypt.CompareHashAndPassword([]byte(reloaded.PasswordHash), []byte("yaochao11")); err != nil {
+		t.Fatalf("new password should work: %v", err)
+	}
+	if reloaded.Phone != "13800001234" {
+		t.Fatalf("existing phone binding should be preserved, got %q", reloaded.Phone)
+	}
+	var memberCount int64
+	if err := db.Model(&model.MerchantMember{}).
+		Where("merchant_id = ? AND user_id = ?", merchantID, staff.ID).
+		Count(&memberCount).Error; err != nil {
+		t.Fatalf("count memberships: %v", err)
+	}
+	if memberCount != 1 {
+		t.Fatalf("membership count = %d, want 1", memberCount)
+	}
+}
+
+func TestAddMemberDoesNotReclaimActiveOrForeignAccount(t *testing.T) {
+	db := newServiceTestDB(t)
+	svc := NewMerchantService(db, nil, NewTenantService(db))
+	merchantA, ownerAUserID := seedMerchantWithOwner(t, db, "reclaim-a", "reclaim-owner-a", 1)
+	merchantB, ownerBUserID := seedMerchantWithOwner(t, db, "reclaim-b", "reclaim-owner-b", 1)
+	seedOperatorRole(t, db, merchantA)
+	seedOperatorRole(t, db, merchantB)
+
+	oldHash, err := bcrypt.GenerateFromPassword([]byte("oldpass123"), bcrypt.DefaultCost)
+	if err != nil {
+		t.Fatalf("hash old password: %v", err)
+	}
+
+	active := model.User{Username: "active-staff", PasswordHash: string(oldHash), Role: model.RoleMerchant, Status: 1}
+	if err := db.Create(&active).Error; err != nil {
+		t.Fatalf("create active staff: %v", err)
+	}
+	if err := db.Create(&model.MerchantMember{
+		MerchantID: merchantA, UserID: active.ID, Role: model.MemberRoleOperator, Status: 1,
+	}).Error; err != nil {
+		t.Fatalf("create active member: %v", err)
+	}
+	if _, err := svc.AddMember(merchantA, AddMemberInput{
+		Username: "active-staff", Password: "newpass123", Role: model.MemberRoleOperator,
+	}, ownerAUserID); err == nil || !strings.Contains(err.Error(), "员工用户名已存在") {
+		t.Fatalf("active account must not be re-added, got %v", err)
+	}
+
+	foreign := model.User{Username: "foreign-staff", PasswordHash: string(oldHash), Role: model.RoleMerchant, Status: 1}
+	if err := db.Create(&foreign).Error; err != nil {
+		t.Fatalf("create foreign staff: %v", err)
+	}
+	foreignMember := model.MerchantMember{
+		MerchantID: merchantA, UserID: foreign.ID, Role: model.MemberRoleOperator, Status: 1,
+	}
+	if err := db.Create(&foreignMember).Error; err != nil {
+		t.Fatalf("create foreign member: %v", err)
+	}
+	if err := db.Model(&foreignMember).Update("status", 0).Error; err != nil {
+		t.Fatalf("disable foreign member: %v", err)
+	}
+	if _, err := svc.AddMember(merchantB, AddMemberInput{
+		Username: "foreign-staff", Password: "newpass123", Role: model.MemberRoleOperator,
+	}, ownerBUserID); err == nil || !strings.Contains(err.Error(), "员工用户名已存在") {
+		t.Fatalf("another merchant must not reclaim the account, got %v", err)
+	}
+
+	var reloaded model.User
+	if err := db.First(&reloaded, foreign.ID).Error; err != nil {
+		t.Fatalf("reload foreign staff: %v", err)
+	}
+	if err := bcrypt.CompareHashAndPassword([]byte(reloaded.PasswordHash), []byte("oldpass123")); err != nil {
+		t.Fatalf("foreign account password must remain unchanged: %v", err)
+	}
+}