Abstract: A speed controller of an electrical car includes a fin emplaced on the base plate of a body, a control circuit board and a drive circuit board connected and emplaced on the top of the fin, and separated by a support bracket. Moreover, an external signal input terminal is located on the body, to facilitate the feeding of external control signal into the control circuit board and the transmission of feedback signal and control signal. For the control circuit, the direction and strength of current of a motor winding are controlled by transistors, and the magnitude of current strength of a motor armature winding is controlled by transistors, using the PWM method. The magnitude of current strength is acquired by a feedback resistor and passed to a CPU, serving as the basis of controlling the direction of current of the motor field winding and the motor speed.