Abstract: In order to study the influence of the wind tunnel ground simulation system in a wind tunnel on aerodynamic testing and to improve the accuracy of automotive wind tunnel test results, a series of experiments, including empty wind tunnel tests and real vehicle tests, were conducted. These tests provided data on the distribution of the ground boundary layer in the test section, the aerodynamic coefficients under different ground simulation conditions, and wake flow fields. The effects and operational mechanisms of the ground simulation system on the aerodynamic testing were studied. The results show that the central belt and the suction system independently influence aerodynamic test results, with the suction system having a more pronounced effect than the central belt. Both the central belt and the suction system increase the drag coefficient when activated. In contrast, they reduce the rear lift coefficient. Meanwhile, the front lift coefficient remains largely unaffected by the central belt but is increased by the suction system, reflecting the different effects of the central belt and the suction system. Overall, the influence of the ground simulation system on the rear lift coefficient is greater than that on the front lift coefficient, resulting in a net reduction of the total lift coefficient.