public ActionResult Create()
        {
           Models.category cat = new Models.category();
            List<SelectListItem> list = cat.GetList().Select(p => new SelectListItem { Text = p.category1, Value = p.ID.ToString() }).ToList();

            list[0].Selected = true;
            ViewData["Category1"] = list;

            Models.subcategory subcat = new Models.subcategory();


            List<SelectListItem> list1 = subcat.GetList().Select(p => new SelectListItem { Text = p.subcategory1, Value = p.ID.ToString() }).ToList();

            list1[0].Selected = true;
            ViewData["Category2"] = list1;
         
            return View();
        }
-------------------------razor view-----------------------------------------------
  <div>
          @{ List<SelectListItem> lstCategories = (List<SelectListItem>)ViewData["category1"]; }
            @Html.DropDownList("dbcat", lstCategories, new { id="dbcat" })
        </div>
        <div>
            @{ List<SelectListItem> lstsubCategories = (List<SelectListItem>)ViewData["Category2"]; }
            @Html.DropDownList("dbsubcat", lstsubCategories, new { id="dbsubcat"})

 public ActionResult SelectCategory(int id)
        {

          
           studentDataContext  db= new studentDataContext();
            var subcat = db.subcategories.Where(m => m.ID == id).Select(c => new
            {
                c.ID,
                c.subcategory1
            });
            return Json(subcat, JsonRequestBehavior.AllowGet);
        }

  <script src="~/Scripts/jquery-1.7.1.min.js"></script> 



<script type="text/javascript">
  
    $('#dbcat').change(function () {
   
    jQuery.getJSON('@Url.Action("SelectCategory")', { id: $(this).attr('value') }, function (data) {
            $('#dbsubcat').empty(); jQuery.each(data, function (i) {
                var option = $('<option></option>')
             .attr("value", data[i].Id).text(data[i].Title); $("#dbcat").append(option);
            });
        });
   });

</script>

$('#dbcat').change(function ()