In order to predict the imaging quality of space cryogenic optical system, a method of high accuracy measuring the wave front aberration of the optical system with low F number and short back focal in cryogenic vacuum environment was presented. Firstly, the optical path was designed. The layout of cryogenic optical system, interferometer and flat mirror were prepared for wave front aberration testing. Then, the key components such as cryogenic vacuum standard lens, standard flat mirror and atmospheric window glass were analyzed and designed. The testing wave front aberration was removed as a system error term. Finally, the wave front aberrations of normal pressure and temperature and cryogenic vacuum environment (Temperature: 100 K, Pressure: 1×10-4 Pa) were obtained by debugging the optical path. The accuracy test showed that the deviation between the measured value and the standard value was 0.010λ(λ=632.8 nm), and the difference was very small, which proved the feasibility of the test method. The wave front aberration difference between the two stages was small. This method solved the difficult problem of the cryogenic vacuum optical system wave front aberration testing with low F number and short back focal in the cryogenic vacuum environment, which couldn′t be accurately tested or even tested.