In order to remedy the situation of selecting optimal number of load in the multi-load wireless power transmission system via magnetic coupling resonance，the theoretical relationship between the total efficiency of the system and the number of the load is established with circuit model. When symmetric and asymmetric arrangement of multiple coils are took into account，the optimal number of load corresponding to the saturated total efficiency is quantitatively calculated，and the influences of coil radius and transmission distance on the selection of the optimal number of load are investigated in detail. The conclusion for optimal number of load mainly depends on the coil radius is obtained. Finally，the simulation platform is built by ADS 2015 and the correctness of theoretical analysis is verified.