The invention provides a vehicle power-assisted braking control method and a device and a vehicle power-assisted braking system. The method comprises: acquiring a pedal stroke signal; filtering the pedal stroke signal to obtain a corresponding pedal stroke curve; determining the basic torque of a motor according to the pedal stroke curve and a preset braking assist ratio; determining the target torque of the motor according to the pedal stroke curve and a motor angle signal; and controlling the control current of the motor according to the target torque to control the output torque of the motor; according to the output torque and the basic torque of the motor, the brake master cylinder is controlled through the transmission mechanism to establish the brake pressure. The braking system hasthe advantages of improving the response speed of the braking system, shortening the braking distance, and being capable of adjusting the braking assist ratio according to the subjective will of a driver, thereby improving the comfort of vehicle braking.