The method comprises: the damaged inputted optical signals are divided into two routes via two output end of optic splitter and coupler; one route of signal is connected to the optic delay line (2) and the non-linear optic signal processor(4); the other route of signal is connected to the optic delay line (3) and the non-linear optic signal processor (5); the non-linear optic signal processor (4)and (5) respectively make phase and amplitude compression for the four phase shift keyed signals orthogonal each other in the angular bisector direction to generate two phase shift keyed signals orthogonal each other; said two route of signals is combined to generate the four phase shift keyed signals via an optical multiplexer. The invention can be used to restore the optical four phase shift keyed signals polluted by noise.