At present, the elimination of headlamp detection error is to straighten the test-waiting vehicle, namely the straightening device makes the vehicle body axis to be right with headlight detector at the distance required. However, the headlamp illumination direction should be the vehicle's driving direction and the perpendicular direction of rear axle is the vehicle's driving direction, so the detection benchmark to headlamp should be the vehicle's driving direction. This paper proposes a new method of error correction of headlamp detection based on bias angle identification of axle placed. Firstly, this paper establishes a tire model, and carries out research on modeling and simulating bias angle of tire, then make error analysis of bias angle identification. Simulation analysis shows that when changes some influence factors, for example tire size, shape, and convex volume, the device is still of high accuracy, so the method is feasible. This paper also establishes the experimental system of detecting axle bias angle, furthermore makes a test and error analysis pointing to the system. The result verifies the simulation conclusions.