A method to extract phase shifts and reconstruct the object wave in generalized phase-shifting interferometry (GPSI) is proposed. The phase distribution of a standard phase object and the least-square method are used to extract phase shifts over a wide range from 0 to π. Consequently, the tested object wave can be further reconstructed with the extracted phase shifts. It is accurate and applicable for GPSI of any frame number N (N ≥ 2). Computer simulation has verified its feasibility and validity.