Abstract: A speed control circuit of a fan motor simultaneously controlled by temperature and PWM signals is provided. The PWM signals are received by a PWM control circuit, which sends a PWM control signal based on duty cycles of the PWM signals to a temperature detecting circuit. The temperature detecting circuit not only receives the PWM control signal and generates a temperature control signal according to the temperature around the fan motor, but also combines both the control signals to send a fan motor speed control signal to an amplifier. Then, the amplifier amplifies the fan motor speed control signal and transmits it to the controllable motor driving circuit. At last, the controllable motor driving circuit transfers the fan motor speed control signal into a fan motor driving signal in order to drive the fan motor.