Abstract: The present invention provides a wireless electrical power transmission system and its control method with good thermal stability. Said system, comprising a transmitting coil frequency generating part and a coil frequency phase tracking and feedback part, the transmitting coil frequency generating part composed of a control circuit, a driving circuit and an inverter circuit, the coil frequency phase tracking and feedback part composed of a frequency detection circuit and a phase locked loop circuit, is characterized in that said control circuit is controlled by software to output two opposite control signals, each of which controls opening and closing of a switch tube after passing through the driving circuit to generate high-frequency oscillation in the coil.