Among electric vehicle charging technologies, wireless charging technology is undoubtedly a most convenient method, also needless to get refreshed and repaired as wires do. Nevertheless, it has long been a tough issue that the efficiency remains low, which causes great waste and too much heat even add to the possibility of fire emergency. Due to low charging efficiency and non-universal charging equipment, wireless charging equipment for electric vehicles has not been effectively promoted. Based on this, integrated circuit theory and electromagnetic field equation, this paper established electromagnetic coupling wireless charging circuit model, based on this model, the maximum wireless charging power transmission efficiency and the maximum horizontal offset and other issues are studied.