The upper limit of location area division is closely related to the service model and the traffic model of location area. Currently, the theoretical value can be worked out by using paging area planning tool. Since 3G service model and traffic model are very complicated, some problems still exist: how big is the difference between preconditions of paging area planning tool and actual cases, how is the agreement of the theoretical value and the actual value, which require further theoretical study and experiences from the network optimization practices.