Off-axis paraboloid (OAP) is widely used in optical system of large diameter, such as astronomical instruments, space optics and so on, for it produce no aberration at geometric focus. It simplifies the structure of optical system, improves imaging quality, reduces the size and weight, also cost of the system. The software Zemax was used to simulate the adjustment errors including high-low and pitch, tilt and off-axis distance, and the rotation around the secondary optical axis, by taking an off-axis paraboloid mirror with the diameter of 400mm, focal length of 4000mm, and the off-axis distance of 350mm for an example. Then the corresponding experiments were performed to verify the simulation results using PhaseCam6000 interferometer of 4D technology. It proves the simulation model in correct, will play an important role in adjusting an off-axis paraboloid mirror.