diff --git a/go/internal/packagesdriver/sizes.go b/go/internal/packagesdriver/sizes.go
index ea15d57be1a..ecce7405c69 100644
--- a/go/internal/packagesdriver/sizes.go
+++ b/go/internal/packagesdriver/sizes.go
@@ -11,6 +11,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"go/types"
+	"golang.org/x/tools/internal/lsp/protocol"
 	"log"
 	"os"
 	"os/exec"
@@ -125,6 +126,7 @@ func InvokeGo(ctx context.Context, env []string, dir string, usesExportData bool
 	cmd.Dir = dir
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr
+	protocol.AdjustGoListForVendorMode(&(cmd.Env), &(cmd.Args))
 	if err := cmd.Run(); err != nil {
 		exitErr, ok := err.(*exec.ExitError)
 		if !ok {
diff --git a/go/packages/golist.go b/go/packages/golist.go
index 8c3594e3796..2a495ec6ef1 100644
--- a/go/packages/golist.go
+++ b/go/packages/golist.go
@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"go/types"
+	"golang.org/x/tools/internal/lsp/protocol"
 	"hash/fnv"
 	"io/ioutil"
 	"log"
@@ -860,7 +861,7 @@ func invokeGo(cfg *Config, args ...string) (*bytes.Buffer, error) {
 	defer func(start time.Time) {
 		cfg.Logf("%s for %v, stderr: <<%s>>\n", time.Since(start), cmdDebugStr(cmd, args...), stderr)
 	}(time.Now())
-
+	protocol.AdjustGoListForVendorMode(&(cmd.Env), &(cmd.Args))
 	if err := cmd.Run(); err != nil {
 		// Check for 'go' executable not being found.
 		if ee, ok := err.(*exec.Error); ok && ee.Err == exec.ErrNotFound {
diff --git a/internal/lsp/cache/session.go b/internal/lsp/cache/session.go
index 3511bb3fec0..8baa7bef95c 100644
--- a/internal/lsp/cache/session.go
+++ b/internal/lsp/cache/session.go
@@ -93,6 +93,11 @@ func (s *session) NewView(ctx context.Context, name string, folder span.URI) sou
 		},
 		ignoredURIs: make(map[span.URI]struct{}),
 	}
+	if enableVendor, ok := ctx.Value("ENABLEVENDOR").(bool); ok && enableVendor {
+		// Set 'GOPROXY=off' to disable the network access
+		v.env = append(v.env, "GOPROXY=off")
+		v.env = append(v.env, "ENABLEVENDOR=on")
+	}
 	// Preemptively build the builtin package,
 	// so we immediately add builtin.go to the list of ignored files.
 	v.buildBuiltinPkg(ctx)
diff --git a/internal/lsp/elasticserver.go b/internal/lsp/elasticserver.go
index b3bffe108de..2ebeedab661 100644
--- a/internal/lsp/elasticserver.go
+++ b/internal/lsp/elasticserver.go
@@ -189,10 +189,8 @@ type WorkspaceFolderMeta struct {
 // manageDeps will try its best to convert the folders to modules. The core functions, like deps downloading and deps
 // management, will be implemented in the package 'cache'.
 func (s ElasticServer) ManageDeps(folders *[]protocol.WorkspaceFolder) error {
-	// Note: For the upstream go langserver, granularity of the workspace folders is repository. But for the elastic go
-	// language server, there are repositories contain multiple modules. In order to handle the modules separately, we
-	// consider different modules as different workspace folders, so we can manage the dependency of different modules
-	// separately.
+	// In order to handle the modules separately, we consider different modules as different workspace folders, so we
+	// can manage the dependency of different modules separately.
 	for _, folder := range *folders {
 		metadata := &WorkspaceFolderMeta{}
 		if folder.URI != "" {
diff --git a/internal/lsp/general.go b/internal/lsp/general.go
index 207aa8e6682..b2d5faa9268 100644
--- a/internal/lsp/general.go
+++ b/internal/lsp/general.go
@@ -38,6 +38,9 @@ func (s *Server) initialize(ctx context.Context, params *protocol.InitializePara
 		if opt, ok := opts["noIncrementalSync"].(bool); ok && opt {
 			s.textDocumentSyncKind = protocol.Full
 		}
+		if opt, ok := opts["installGoDependency"].(bool); ok && opt {
+			s.installGoDependency = true
+		}
 	}
 
 	// Default to using synopsis as a default for hover information.
diff --git a/internal/lsp/protocol/elasticserver.go b/internal/lsp/protocol/elasticserver.go
index cdcaab39260..f9425249feb 100644
--- a/internal/lsp/protocol/elasticserver.go
+++ b/internal/lsp/protocol/elasticserver.go
@@ -14,6 +14,22 @@ type ElasticServer interface {
 	ManageDeps(folders *[]WorkspaceFolder) error
 }
 
+func AdjustGoListForVendorMode(env *[]string, args *[]string) {
+	l := len(*env)
+	for i := range *env {
+		if (*env)[l-i-1] == "ENABLEVENDOR=on" {
+			// If 'ENABLEVENDOR' is on, append '-mod=vendor' to go list command
+			for j := range *args {
+				if (j+2 < len(*args)) && (*args)[j] == "go" && (*args)[j+1] == "list" {
+					*args = append((*args)[:j+2], append([]string{"-mod=vendor"}, (*args)[j+2:]...)...)
+					break
+				}
+			}
+			return
+		}
+	}
+}
+
 type elasticServerHandler struct {
 	canceller
 	server ElasticServer
diff --git a/internal/lsp/server.go b/internal/lsp/server.go
index 6ab758b6c05..3a738093eab 100644
--- a/internal/lsp/server.go
+++ b/internal/lsp/server.go
@@ -88,6 +88,7 @@ type Server struct {
 	preferredContentFormat        protocol.MarkupKind
 	disabledAnalyses              map[string]struct{}
 	wantSuggestedFixes            bool
+	installGoDependency           bool
 
 	supportedCodeActions map[source.FileKind]map[protocol.CodeActionKind]bool
 
diff --git a/internal/lsp/workspace.go b/internal/lsp/workspace.go
index 58127569001..214d69662f3 100644
--- a/internal/lsp/workspace.go
+++ b/internal/lsp/workspace.go
@@ -8,8 +8,10 @@ import (
 	"context"
 
 	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/lsp/telemetry/log"
 	"golang.org/x/tools/internal/span"
 	errors "golang.org/x/xerrors"
+	"os/exec"
 )
 
 func (s *Server) changeFolders(ctx context.Context, event protocol.WorkspaceFoldersChangeEvent) error {
@@ -31,6 +33,16 @@ func (s *Server) changeFolders(ctx context.Context, event protocol.WorkspaceFold
 }
 
 func (s *Server) addView(ctx context.Context, name string, uri span.URI) error {
+	if s.installGoDependency {
+		cmd := exec.Command("go", "mod", "download")
+		cmd.Dir = uri.Filename()
+		if err := cmd.Run(); err != nil {
+			log.Error(ctx, "failed to download the dependencies", err)
+		}
+	} else {
+		// If we disable the go dependency download, trying to find the deps from the vendor folder.
+		ctx = context.WithValue(ctx, "ENABLEVENDOR", true)
+	}
 	view := s.session.NewView(ctx, name, uri)
 	s.stateMu.Lock()
 	state := s.state