Wireless charging technology is a kind of power transmission technology using wireless technology. First of all,researched the basic working principle of the wireless charger, and then in view of the wireless charger charging efficiency is low, the charging efficiency of single coil and three coils wireless chargers at different sidetrack distances is analyzed and compared. The analysis results show that single coil charging efficiency is higher, and the charging efficiency of three coils charger is more stable,which provides a theoretical basis for the design of multi-coil charger.