1.If YOu are binding grid in code behind refer this
http://msdn.microsoft.com/en-us/library/system.data.dataview.rowfilter.aspx
2.If you are using SqlDatsource
<asp:textbox id="contractID" runat="server" >duration</asp:textbox>
<asp:textbox id="duration" runat="server" >duration</asp:textbox>
<asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1">
</asp:GridView>
<br />
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
SelectCommand="SELECT DISTINCT * FROM [Contract]" FilterExpression="contractID LIKE '{0}%' AND duration LIKE '{1}%'">
<FilterParameters>
<asp:ControlParameter ControlID="contractID" Name="contractID"
PropertyName="Text" Type="String" />
<asp:ControlParameter ControlID="duration" Name="duration" PropertyName="Text"
Type="String" />
</FilterParameters>
</asp:SqlDataSource>