Abstract: A frequency and speed modulating method has been applied to the blower motor of heat medium heater. The method, by modulating the frequency and speed of electric motor, can realize the optimizing control of the operating process of heat medium heater, which saves electricity energy and fuel oil. Through modulating frequency and speed, controlling the start-up current, running in high/low speed without any shock, frequent start-up and shut down can be realized. The principle of frenquency and speed modulating and the system composition are introduced.