diff --git a/net/apps/multithread_downloader/control.go b/net/apps/multithread_downloader/control.go
index ad9ec32..c687dfb 100644
--- a/net/apps/multithread_downloader/control.go
+++ b/net/apps/multithread_downloader/control.go
@@ -12,27 +12,71 @@ var (
 
 const (
 	DefaultMaxThread       = 32
-	DefaultMaxThreadPerURL = 8
+	DefaultMaxThreadPerReq = 8
 )
 
 type Client struct {
-	Client        *http.Client
-	MaxThread     uint64
-	currentThread uint64
+	Transport   *http.Transport
+	distributor *Distributor
+	tasks       []*Downloader
 }
 
 func NewClient(opts ...Option) *Client {
 	client := &Client{
-		Client:        &http.Client{},
-		MaxThread:     DefaultMaxThread,
-		currentThread: 0,
+		Transport: nil,
+		distributor: &Distributor{
+			running:         true,
+			MaxThread:       DefaultMaxThread,
+			MaxThreadPerReq: DefaultMaxThreadPerReq,
+			currentThread:   0,
+			acquire:         make(chan uint),
+			getter:          make(chan uint),
+			release:         make(chan uint),
+		},
+		tasks: make([]*Downloader, 0),
 	}
 	for _, opt := range opts {
 		opt(client)
 	}
+	go client.distributor.routine()
 	return client
 }
 
-func (d *Client) Download(url *url.URL, file *os.File, opts ...Option) {
+// Download 异步提交一个下载任务
+func (c *Client) Download(
+	URL string, file string, header http.Header,
+) (*Downloader, error) {
+	targetURL, err := url.Parse(URL)
+	if err != nil {
+		return nil, err
+	}
+	osFile, err := os.OpenFile(file, os.O_CREATE, os.ModePerm)
+	if err != nil {
+		return nil, err
+	}
+	downloader := createDownloader(c, osFile, targetURL, header)
+	go downloader.head(c.distributor)
+	c.tasks = append(c.tasks, downloader)
+	return downloader, nil
+}
 
+func (distri *Distributor) routine() uint {
+	for distri.running {
+		select {
+		case acquire := <-distri.acquire:
+			switch free := distri.MaxThread - distri.currentThread; {
+			case free >= acquire:
+				distri.currentThread += acquire
+				distri.getter <- acquire
+			case free <= 0:
+				release := <-distri.release
+				distri.getter <- release
+			default:
+				distri.currentThread += free
+
+			}
+		case release := <-distri.release:
+
+		}
+	}
 }
diff --git a/net/apps/multithread_downloader/distributor.go b/net/apps/multithread_downloader/distributor.go
new file mode 100644
index 0000000..55f7925
--- /dev/null
+++ b/net/apps/multithread_downloader/distributor.go
@@ -0,0 +1,11 @@
+package mdown
+
+type Distributor struct {
+	running         bool
+	MaxThread       uint
+	MaxThreadPerReq uint
+	currentThread   uint
+	release         chan uint
+	acquire         chan uint
+	getter          chan uint
+}
diff --git a/net/apps/multithread_downloader/downloader.go b/net/apps/multithread_downloader/downloader.go
new file mode 100644
index 0000000..2ba8c1e
--- /dev/null
+++ b/net/apps/multithread_downloader/downloader.go
@@ -0,0 +1,75 @@
+package mdown
+
+import (
+	`net/http`
+	`net/url`
+	`os`
+	`strconv`
+)
+
+type Downloader struct {
+	client       *http.Client
+	targetURL    *url.URL
+	file         *os.File
+	headers      http.Header
+	ContentSize  int
+	AcceptRanges bool
+	State        State
+	threads      []*worker
+}
+type State int
+
+const (
+	FAILED State = iota - 1
+	WAITING
+	DOWNLOADING
+	SUCCESS
+)
+
+func createDownloader(
+	client *Client, file *os.File, URL *url.URL, header http.Header,
+) *Downloader {
+	downloader := &Downloader{
+		&http.Client{
+			Transport: client.Transport,
+		},
+		URL,
+		file,
+		header,
+		0,
+		false,
+		WAITING,
+		nil,
+	}
+	return downloader
+}
+
+func (d *Downloader) head(distri *Distributor) {
+	headQuery := &http.Request{
+		Method: "HEAD",
+		URL:    d.targetURL,
+		Header: d.headers,
+	}
+	resp, err := d.client.Do(headQuery)
+	if err != nil {
+		d.State = FAILED
+		return
+	}
+	defer func() {
+		_ = resp.Body.Close()
+	}()
+	contentLength := resp.Header.Get("content-length")
+	if d.ContentSize, err = strconv.Atoi(contentLength); contentLength == "" || err != nil {
+		d.State = FAILED
+		return
+	}
+	acceptRanges := resp.Header.Get("accept-ranges")
+	d.AcceptRanges = acceptRanges == "bytes"
+	d.State = WAITING
+	client.acquire(client.)
+	d.generator()
+}
+
+func (d *Downloader) generator(thread uint) {
+
+}
\ No newline at end of file
diff --git a/net/apps/multithread_downloader/option.go b/net/apps/multithread_downloader/option.go
index 9ae0b1b..38cbb4f 100644
--- a/net/apps/multithread_downloader/option.go
+++ b/net/apps/multithread_downloader/option.go
@@ -9,14 +9,26 @@ type Option func(*Client)
 
 func WithTransportProxy(proxyURL *url.URL) Option {
 	return func(client *Client) {
-		client.Client.Transport = &http.Transport{
+		client.Transport = &http.Transport{
 			Proxy: http.ProxyURL(proxyURL),
 		}
 	}
 }
 
 func WithMaxThread(count int) Option {
+	if count < 0 {
+		panic("count must be greater than zero")
+	}
+	return func(client *Client) {
+		client.distributor.MaxThread = uint(count)
+	}
+}
+
+func WithMaxThreadPerReq(count int) Option {
+	if count <= 0 {
+		panic("count must be greater than zero")
+	}
 	return func(client *Client) {
-		client.MaxThread = uint64(count)
+		client.distributor.MaxThreadPerReq = uint(count)
 	}
 }