Built-in load switch of smart electricity meter is an important guarantee to achieve the "complete fee control" target in smart grid. The existing control method of smart electricity meter built-in load switch is only based on users’ payment situation, while doesn’t consider the actual situation of the users’ load. If high current passes through contacts in the moment of the load switch breaking, it’s extremely easy to cause arc which may trigger contacts welding or even burning. This paper proposes an optimal control mechanism of single-phase smart electricity meter built-in load switch which takes the realization of "complete fee control" function, users’ load current and load power factor into account. Through comparison test, it is proved that the optimal control mechanism can significantly improve the electrical life of load switch and ensure the safety as well as the stability of power system.