The invention discloses an anti-backward motion device of cars. The anti-backward motion device comprises a frame connection portion and a stretching anti-thrust portion, wherein the frame connection portion is a main body frame with a lower opening, the extension anti-thrust portion comprises a slide block, a first drive mechanism, a stop block, a second drive mechanism, a first rotating mechanism and a second rotating mechanism, the slide block is connected with an opening end of the main body frame in a sliding manner, the first drive mechanism drives the slide block to move horizontally, the stop block moves together with the slide block, the second drive mechanism drives the stop block to stretch, the first rotating mechanism drives the second drive mechanism to rotate, and the second rotating mechanism drives the stop block to rotate. The anti-backward motion device is improved on the basis of the original frame of the car, the motor can be powered by an operator through an operation switch, the motor can drive a hydraulic lever to swing up and down for a given angle to extend out a secondary hydraulic lever, and the position of a wedge block on the front section can be adjusted by virtue of a stepper motor on the wedge block, so that the car is at a parking safety state, and the backward motion of the car when the car is stopped and started on a ramp can be effectively prevented.