Both the amplitude error and phase error retrieved in the recording plane in phase-shifting interferometry (PSI) have effects on the reconstructed wave-front in original object plane placed a distance away. We have proposed a simple and effective algorithm, which can simultaneously correct both kinds of wave errors caused by arbitrary and unequal phase shift errors in PSI for an off-lying object and then greatly improve the reconstructed object wave-front by digital image processing based on the statistic nature of diffraction field. The principles are explained, and a series of computer simulations are made to verify its feasibility.