I solve it by self !<br />
public List<items> SearchItemsByCategory(int categoryid )
{
var items= (from i in db.Items
join ic in db.ItemsCommon.Where(x=>x.CategoryId == categoryid )
on i.ItemsId equals ic.ItemsId
into tempJoin
from t2 in tempJoin.DefaultIfEmpty()
select new { i.ItemsId,Name_En = t2==null?i.Name_En: t2.Name_En }).ToList();
return items;
}</items>