diff --git a/models/issue_milestone.go b/models/issue_milestone.go
index b1505c12cb1..f8f414e7166 100644
--- a/models/issue_milestone.go
+++ b/models/issue_milestone.go
@@ -7,7 +7,6 @@ package models
 import (
 	"fmt"
 
-	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/timeutil"
@@ -394,46 +393,6 @@ func ChangeMilestoneAssign(issue *Issue, doer *User, oldMilestoneID int64) (err
 	if err = sess.Commit(); err != nil {
 		return fmt.Errorf("Commit: %v", err)
 	}
-
-	var hookAction api.HookIssueAction
-	if issue.MilestoneID > 0 {
-		hookAction = api.HookIssueMilestoned
-	} else {
-		hookAction = api.HookIssueDemilestoned
-	}
-
-	if err = issue.LoadAttributes(); err != nil {
-		return err
-	}
-
-	mode, _ := AccessLevel(doer, issue.Repo)
-	if issue.IsPull {
-		err = issue.PullRequest.LoadIssue()
-		if err != nil {
-			log.Error("LoadIssue: %v", err)
-			return
-		}
-		err = PrepareWebhooks(issue.Repo, HookEventPullRequest, &api.PullRequestPayload{
-			Action:      hookAction,
-			Index:       issue.Index,
-			PullRequest: issue.PullRequest.APIFormat(),
-			Repository:  issue.Repo.APIFormat(mode),
-			Sender:      doer.APIFormat(),
-		})
-	} else {
-		err = PrepareWebhooks(issue.Repo, HookEventIssues, &api.IssuePayload{
-			Action:     hookAction,
-			Index:      issue.Index,
-			Issue:      issue.APIFormat(),
-			Repository: issue.Repo.APIFormat(mode),
-			Sender:     doer.APIFormat(),
-		})
-	}
-	if err != nil {
-		log.Error("PrepareWebhooks [is_pull: %v]: %v", issue.IsPull, err)
-	} else {
-		go HookQueue.Add(issue.RepoID)
-	}
 	return nil
 }
 
diff --git a/routers/api/v1/repo/issue.go b/routers/api/v1/repo/issue.go
index 402da82f078..6f502a5abd3 100644
--- a/routers/api/v1/repo/issue.go
+++ b/routers/api/v1/repo/issue.go
@@ -19,6 +19,7 @@ import (
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/modules/util"
+	milestone_service "code.gitea.io/gitea/services/milestone"
 )
 
 // ListIssues list the issues of a repository
@@ -345,7 +346,7 @@ func EditIssue(ctx *context.APIContext, form api.EditIssueOption) {
 		issue.MilestoneID != *form.Milestone {
 		oldMilestoneID := issue.MilestoneID
 		issue.MilestoneID = *form.Milestone
-		if err = models.ChangeMilestoneAssign(issue, ctx.User, oldMilestoneID); err != nil {
+		if err = milestone_service.ChangeMilestoneAssign(issue, ctx.User, oldMilestoneID); err != nil {
 			ctx.Error(500, "ChangeMilestoneAssign", err)
 			return
 		}
diff --git a/routers/api/v1/repo/pull.go b/routers/api/v1/repo/pull.go
index 5ac542ec207..7be34c656e8 100644
--- a/routers/api/v1/repo/pull.go
+++ b/routers/api/v1/repo/pull.go
@@ -18,6 +18,7 @@ import (
 	"code.gitea.io/gitea/modules/pull"
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/timeutil"
+	milestone_service "code.gitea.io/gitea/services/milestone"
 )
 
 // ListPullRequests returns a list of all PRs
@@ -402,7 +403,7 @@ func EditPullRequest(ctx *context.APIContext, form api.EditPullRequestOption) {
 		issue.MilestoneID != form.Milestone {
 		oldMilestoneID := issue.MilestoneID
 		issue.MilestoneID = form.Milestone
-		if err = models.ChangeMilestoneAssign(issue, ctx.User, oldMilestoneID); err != nil {
+		if err = milestone_service.ChangeMilestoneAssign(issue, ctx.User, oldMilestoneID); err != nil {
 			ctx.Error(500, "ChangeMilestoneAssign", err)
 			return
 		}
diff --git a/routers/repo/issue.go b/routers/repo/issue.go
index dc09a650fed..4ae791221cf 100644
--- a/routers/repo/issue.go
+++ b/routers/repo/issue.go
@@ -26,6 +26,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	api "code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/util"
+	milestone_service "code.gitea.io/gitea/services/milestone"
 
 	"github.com/unknwon/com"
 )
@@ -1086,7 +1087,7 @@ func UpdateIssueMilestone(ctx *context.Context) {
 			continue
 		}
 		issue.MilestoneID = milestoneID
-		if err := models.ChangeMilestoneAssign(issue, ctx.User, oldMilestoneID); err != nil {
+		if err := milestone_service.ChangeMilestoneAssign(issue, ctx.User, oldMilestoneID); err != nil {
 			ctx.ServerError("ChangeMilestoneAssign", err)
 			return
 		}
diff --git a/services/milestone/milestone.go b/services/milestone/milestone.go
new file mode 100644
index 00000000000..68052e5a6ce
--- /dev/null
+++ b/services/milestone/milestone.go
@@ -0,0 +1,59 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package models
+
+import (
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/log"
+	api "code.gitea.io/gitea/modules/structs"
+)
+
+// ChangeMilestoneAssign changes assignment of milestone for issue.
+func ChangeMilestoneAssign(issue *models.Issue, doer *models.User, oldMilestoneID int64) (err error) {
+	if err = models.ChangeMilestoneAssign(issue, doer, oldMilestoneID); err != nil {
+		return
+	}
+
+	var hookAction api.HookIssueAction
+	if issue.MilestoneID > 0 {
+		hookAction = api.HookIssueMilestoned
+	} else {
+		hookAction = api.HookIssueDemilestoned
+	}
+
+	if err = issue.LoadAttributes(); err != nil {
+		return err
+	}
+
+	mode, _ := models.AccessLevel(doer, issue.Repo)
+	if issue.IsPull {
+		err = issue.PullRequest.LoadIssue()
+		if err != nil {
+			log.Error("LoadIssue: %v", err)
+			return
+		}
+		err = models.PrepareWebhooks(issue.Repo, models.HookEventPullRequest, &api.PullRequestPayload{
+			Action:      hookAction,
+			Index:       issue.Index,
+			PullRequest: issue.PullRequest.APIFormat(),
+			Repository:  issue.Repo.APIFormat(mode),
+			Sender:      doer.APIFormat(),
+		})
+	} else {
+		err = models.PrepareWebhooks(issue.Repo, models.HookEventIssues, &api.IssuePayload{
+			Action:     hookAction,
+			Index:      issue.Index,
+			Issue:      issue.APIFormat(),
+			Repository: issue.Repo.APIFormat(mode),
+			Sender:     doer.APIFormat(),
+		})
+	}
+	if err != nil {
+		log.Error("PrepareWebhooks [is_pull: %v]: %v", issue.IsPull, err)
+	} else {
+		go models.HookQueue.Add(issue.RepoID)
+	}
+	return nil
+}