不要将该子控件添加到面板中，而是将其添加到应该为父控件的控件中:

HtmlGenericControl divcontrol = new HtmlGenericControl();divcontrol.Attributes[class"] =sxro sx1co"；divcontrol.TagName = "div";pnlUserSearch.Controls.Add(divcontrol);标签问题 = new Label();questionDescription.Text = "text";divcontrol.Controls.Add(问题);//添加到新的 div，而不是面板

I want to add HTML structure and control like this from code behind into a panel

<div class='Main'>
    <div class='cst'>
        First Name
    </div>
    <div class='csc'>
        <asp:Label ID="lblFirstName" CssClass="ronly" runat="server"></asp:Label>
    </div>
    <div class='cst'>
        First Name
    </div>
    <div class='csc'>
        <asp:Label ID="lblFirstName" CssClass="ronly" runat="server"></asp:Label>
    </div>        <div class='cst'>
        First Name
    </div>
    <div class='csc'>
        <asp:Label ID="lblFirstName" CssClass="ronly" runat="server"></asp:Label>
    </div>
    <div class='end'>
    </div>
</div>

  <asp:Panel runat="server" CssClass="sxpnl" ID="pnlUserdata">
        </asp:Panel>

If i try to add like this

 HtmlGenericControl divcontrol = new HtmlGenericControl();
 divcontrol.Attributes["class"] = "sxro sx1co";
 divcontrol.TagName = "div";
 pnlUserSearch.Controls.Add(divcontrol);
 Label question = new Label();
 questionDescription.Text = "text";
 pnlUserSearch.Controls.Add(question);

It will add controls one after another, how can i make controls go nested like that as shown above.

Don't add that child control to the panel, add it to the control that should be the parent:

HtmlGenericControl divcontrol = new HtmlGenericControl();
divcontrol.Attributes["class"] = "sxro sx1co";
divcontrol.TagName = "div";
pnlUserSearch.Controls.Add(divcontrol);

Label question = new Label();
questionDescription.Text = "text";
divcontrol.Controls.Add(question); // add to the new div, not to the panel