首先head标签上添加runat="server"。

 protected void Page_Load(object sender, EventArgs e)
 {
         HtmlGenericControl autoCompleteScript = new HtmlGenericControl("script");
         autoCompleteScript.Attributes.Add("type", "text/javascript");
         autoCompleteScript.Attributes.Add("src", "/js/autocomplete/jquery.autocomplete.js");
         Page.Header.Controls.Add(autoCompleteScript);
 
         HtmlLink autoCompleteCss = new HtmlLink();
         autoCompleteCss.Href = "/js/autocomplete/jquery.autocomplete.css";
         autoCompleteCss.Attributes.Add("rel", "stylesheet");
         autoCompleteCss.Attributes.Add("type", "text/css");
         Page.Header.Controls.Add(autoCompleteCss);
 }