sandbox solution

http://msdn.microsoft.com/en-us/library/ff798382.aspx

Cascadin Dropdown in Sharepoint2010

Down Load Js file from this Link
http://www.c-sharpcorner.com/uploadfile/Roji.Joy/cascading-dropdown-in-share-point-using-jquery/

<script language="javascript" type="text/javascript" src="../../jQuery%20Libraries/jquery-1.8.2.js"></script>
<script language="javascript" type="text/javascript" src="../../jQuery%20Libraries/jquery.SPServices-0.7.2.min.js"></script>
<script language="javascript" type="text/javascript">
$(document).ready(function() {
  $().SPServices.SPCascadeDropdowns({
    relationshipList: "Regions",
    relationshipListParentColumn: "Country",
    relationshipListChildColumn: "Title",
    CAMLQuery: "<Eq><FieldRef Name='Status'/><Value Type='Text'>Active</Value></Eq>",   parentColumn: "Country",
    childColumn: "Region",
    debug: true
  });
  $().SPServices.SPCascadeDropdowns({
    relationshipList: "States",
    relationshipListParentColumn: "Region_x0020_Name",
    relationshipListChildColumn: "Title",
    relationshipListSortColumn: "ID",
    parentColumn: "Region",
    childColumn: "State"
  });
});
</script>


Fore More info ref links..
http://basquang.wordpress.com/2010/09/21/spservices-cascading-drop-down-list-in-sharepoint-2010-list-using-jquery/