I'm gonna use JQuery files in my custom ServerControl , thus I have to add below line within Head tag.
<script type="text/javascript" src="jquery-1.4.3.min.js"></script>
How can I do it in ServerControl with C#
You can register custom scripts using the ClientScriptManager.RegisterClientScriptInclude Method during the page load. Alternatively, you can just include the script in your .aspx page. If this is a public server control, the first method is probably more preferable.
EDIT: alternatively you can register scripts in the <head> tag of the page as follows:
HtmlGenericControl jqueryInclude = new HtmlGenericControl("script");
jqueryInclude.Attributes.Add("type", "text/javascript");
jqueryInclude.Attributes.Add("src", "http://<path to jQuery>");
Page.Header.Controls.Add(jqueryInclude);
来源：https://stackoverflow.com/questions/4117712/add-script-tag-within-head-tag-in-servercontrol-asp-net