Sharepoint LookUp field issue

The below solution will help you while moving the lists which are having the lookups fileds from one site to number sites.

public const string Parent_Child_LookUpFieldName = "LookupFieldName";
public const string CustomParentList = "ParentList";
public const string CustomChildList = "ChildList";

FixLookupFieldsInList(Parent_Child_LookUpFieldName, currentWeb.Lists[CustomParentList], currentWeb.Lists[CustomChildList]);
#region FixLookupFieldsInList
/// 

/// FUNCTION        : FixLookupFieldsInList
/// PURPOSE         : To fix the LookupFields in a list imported using a stp file
/// PARAMETERS      : currentWeb -> current web
///                   fieldName -> The column name to be fixed
///                   list -> The list to be fixed
///                   targetList -> Then list to which the fieldName must reference
/// RETURNS         : None
/// ---------------------------------------------------------------------
/// 
public static void FixLookupFieldsInList(string fieldName, SPList list, SPList targetList)
{
 try
 {
   list.ParentWeb.AllowUnsafeUpdates = true;
   if (list.Fields.ContainsField(fieldName))
   {                    
    SPFieldLookup field = (SPFieldLookup)list.Fields[fieldName];
    //check if the field link to the list is broken. 
    if (field.LookupList != targetList.ID.ToString())
    {
     //copy the schema from the field
     string newFieldXml = field.SchemaXml;
     string oldsourceid = field.LookupList;
     //put the ID of the current list as the source for the lookup
     field.SchemaXml = newFieldXml.Replace(oldsourceid, "{" + targetList.ID.ToString() + "}");
    }
   }
 }
 catch (Exception ex)
 {
  //Error Handling Code
 }
 finally
 {
   list.ParentWeb.AllowUnsafeUpdates = false;
 }
}
#endregion

Happy coding...