Based on third-order aberration theory,a method of null test using compensation that include three compensating lens and a field lens is put forward for paraboloid mirror with super relative aperture,and describes detailed the design process of compensation system.The testing system is designed successfully for a paraboloid mirror that relative aperture is F0.6 and aperture is Φ290 mm. The result of design show that aberration of testing system is well corrected and the system reached to diffraction limit.