In recent years, the optical element with large diameter, large asphericity, fast focal ratio, high-order aspheric has been used in astronomical optics, space optics and space target detection and recognition with ground-based systems and other fields more and more widely. At present we commonly use null lens testing system or partial compensation system with eliminating return error process to test such optical elements. Among them, partial compensation system with eliminating return error process is complex and lack of testing intuitiveness, and the measurement accuracy cannot be guaranteed. Therefore, in the testing of some mirror with very high surface error precision requirement, this method is not applicable. Base on the test of concave high-order aspherical mirror with diameter of 1020 mm, coke ratio of 1/0.5, aspherical degree of 1.8 mm, high-order term of 6, an idea to design zero compensation testing light path by stages is proposed, which can satisfy the requirement of different stages of developing and testing such as rough polishing, fine polishing, interferometer testing. Final, its surface accuracy achieves λ/50.