DataGrid中:
DataFormatString="{0:d}"
eg:
<asp:BoundColumn HeaderText="注册时间" DataFormatString="{0:d}" DataField="RegisterTime" ReadOnly="True" >

DataList中:
<%# DataBinder.Eval(Container.DataItem,"格式化的字段"),"{0:yyyy-MM-dd")%>
eg:
<%#DataBinder.Eval(Container.DataItem, "PC_Time", "{0:yyyy-MM-dd HH:mm}")%>