while click on excel button,title is displayed in excel,but title size is too small, How I can increase the size of title ?
You'd need to use the customize callback from the excelHtml5 button type to modify the XML that is generated for the spreadsheet. You'd need to refer to the open spreadsheet documentation to understand how it all fits together and how to add a new style, as that documentation is outside the scope of DataTables' own documentation.
It looks like you're new here. If you want to get involved, click one of these buttons!