There is a very complex flow structure between two parallel arrangement lifting body vehicles and the structure changes rapidly with the relative position and attitude. The complex aerodynamic interference effects caused by boundary layer/boundary layer, shockwave/boundary layer interference and shock wave/shock wave interferences severely affect the safety of interstage separation. To verify the two-stage parallel separation simulation program and study the variation law of two-stage interference aerodynamic forces, a series of numerical and experimental comparative studies were conducted at the speed of M= 3. Overall, the numerical values are in good agreement with the experimental results. Furthermore, to improve the accuracy of data from CTS tests, support interference, CTS test step size, Reynolds number and other factors were analyzed. The results indicate that the impact of support interference on the experimental results is relatively small and can be ignored in this experiment. In the CTS test, the time step size is usually gradually increased as the distance between the two stages increases for efficiency. However, numerical results show that as the time step size gradually increases, the accuracy of data will be damaged. Due to the large scale of the model, the Reynolds number in the test will be lower than that in flight. The numerical results show that the difference of Reynolds number mainly affects the axial displacement of the two stages, and has little effect on normal motion and attitude angle.