The invention belongs to the technical field of detection methods of automobile brake performance, and particularly relates to a rack-based braking force detection device and a rack-based braking force detection method capable of automatically adjusting automobile axle load. The rack-based braking force detection device capable of automatically adjusting automobile axle load includes an automobile axle load brake test bed, two same lifting platforms, a data collecting and processing system and a control system, wherein the two same lifting platforms are uniformly positioned on the front and rear sides of the automobile axle load brake test bed. The rack-based braking force detection method capable of automatically adjusting automobile axle load includes the following steps of 1, setting devices in the data collecting and processing system to be zero, and collecting axle load and braking force signals; 2, automatically adjusting the heights of undetected wheels on the lifting platforms; 3, detecting the braking force of a measured axle of a vehicle. According to the rack-based braking force detection device and method capable of automatically adjusting automobile axle load, the heights of the lifting platforms of the automobile axle load brake test bed are automatically adjusted, so that the braking effect of the vehicle on an actual level road can be truly simulated on the automobile axle load brake test bed, and the braking performance of the vehicle can be accurately detected.