The generator rotor eccentricity is a common phenomenon， and severe rotor eccentricity will affect the proper operation of that ground fault（GF） protection. Concerned with the impacts generated by rotor-to-ground capacitance on rotor one point GF protection， a method with adjustable two periods injecting square wave rotor GF protection is proposed. By adjusting the period of square wave polarity transformation， the rotor one point GF false alarm caused by the rotor-to-ground capacitance is avoided. By adjusting the direct current component of sampling computation window period， the rotor one point GF alarm caused by the rotor eccentricity is thus avoided. This method plays a good inhibitory effect to one point GF false alarm for all kinds of generator units due to the rotor-to-ground capacitance or the rotor eccentricity， which could solve unstable operation problem of rotor one point GF.