A fixed phase displacement exists when electronic instrument transformers sample analog signals,which affects the measurement accuray,and needs to be corrected using phase shift method.This paper proposes a digital phase-shift method based on least-square fitting algorithm.The digital phase shifting recurrence formula is deduced,and the performance of phase shifting algorithm is simulated and analyzed.The results show that the method has a relatively high resolution and precision in phase-shifting,furthermore,it can guarantee the amplitude measurement accuracy.The algorithm is applied to the Rogowski coil based electronic instrument transformers,and the feasibility and validity of the algorithm are verified by accuracy comparison test.