Abstract: With the stator earth fault protection applying on large scale generator gradually, a method of stator earth fault protection with voltage injection based on multi stage phase compensation is presented to measure the insulating resistance of stator accurately in this paper. By summarizing some experiments and operations of stator earth fault protection with voltage injection recently, the reason that the phase of the injected 20Hz voltage and current signals deviate in different operating condition is analyzed, and it is verified by test. In the end, the multi stage phase compensation method is proposed, which can assure the measurement precision under multiple operating conditions, and is applied in real projects practically. It can be seen from application that the measuring accuracy of stator insulating resistance is enhanced, which has practical value.