一、前台 document.getElementById("Button1").click();

<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />

后台代码 protected void Button1_Click(object sender, EventArgs e)
          {
                  Response.Write("模拟点击");
           }

二、

<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />

<input id="Button1" type="button" name="Button1" value="按钮" onclick="javascript:__doPostBack('Button1','')">