Lateral shearing interferometer can achieve ultra-high-precision measurement of the optical system aberration. It is currently an important component content of the projection lens development. Two main factors affecting lateral shearing interferometry measurement accuracy are 0th order effect and phase shift error. Therefore, a thirteen-step phase restoration algorithm in phase shearing interferometry is proposed. It can 0th zeroth order effect and greatly reduce the phase shifting error demanding. Analysis shows that when the phase shift error is not more than 25° the phase restoration error is less than 0.01° (2.8×10-5λ). For λ=193.386 nm, wavefront restoration error is less than 0.005 nm. Thus, by system error correction wavefront measurement of projection lens of phase shearing interferometer can achieve sub-nanometer accuracy.