The invention relates to a flat plate braking-based lateral force testing device and a flat plate braking-based lateral force testing method. The device comprises a braking force and lateral force testing device, a data acquisition and processing system and a control system. With the device of the invention adopted, a braking force and a lateral force in an emergency braking process of an automobile can be measured in real time, tendency to deviation, sideslip and rollover is analyzed and evaluated, and the braking performance of the automobile can be detected more accurately, and the stability of the automobile in braking can be reasonably evaluated. The device of the invention can be widely applied to an automobile safety inspection station and is of great practical significance for safety driving control of the automobile.