Three-position absolute surface testing technology can be simplified to method of two-position surface testing under some certain conditions.Based on the study of three-position absolute surface testing technology,a new method of two-position spherical testing via Fizeau interferometer is proposed.The method respectively assumes that the surface error of reference surface or test surface only contains aberrations with even symmetry.Results show that λ/30 PVr surface error can be measured though two-position testing as well as the method is repeatable to λ/300 PVr and λ/4000 RMS.Besides,the distribution of surface error measured through two-position testing is very close to one measured though three-position testing.The PVr difference is less than λ/300 and the RMS difference is less than λ/2500.So under certain assumptions,experimental device and process can be simplified through two-position testing method,while the accuracy and repeatability can be maintained.