Suppose you have a DataGrid with several columns full of data. The DataGrid contains several pages. You can disable paging and export all the data to Excel using the RenderControl method:

//export to excelDataGrid_Dimension.AllowPaging = false;BindGrid();Response.Clear();Response.Buffer= true;Response.ContentType = "application/vnd.ms-excel";Response.Charset = "";this.EnableViewState = false;System.IO.StringWriter oStringWriter = new System.IO.StringWriter();System.Web.UI.HtmlTextWriter oHtmlTextWriter =    new System.Web.UI.HtmlTextWriter(oStringWriter);this.ClearControls(DataGrid_Dimension);DataGrid_Dimension.RenderControl(oHtmlTextWriter);Response.Write(oStringWriter.ToString());Response.End();