The invention discloses a generator stator ground protection method. A protective device measures zero sequence voltage at the generator side and the main transformer high-voltage side and calculates fundamental wave effective values Ug0 and Uh0. When Ug0 is larger than the definite value 1, and Uh0 is smaller than the definite value 2, a generator stator ground fault is judged, and protection is achieved by acting on trip after short-time delay tset1. When Uh0 is larger than or equal to the definite value 2, a main transformer high-voltage side ground fault is judged, and generator stator ground protection is locked. After the zero sequence voltage at the main transformer high-voltage side disappears, if Ug0 is reduced continuously, a locking criterion is returned after delay tset2 to prevent misoperation of generator stator ground protection; if Ug0 is kept unchanged or continuously increased, the locking criterion is opened. The generator stator ground fault can be detected sensitively, and action delay is short. The generator stator ground protection method is high in selectivity, if the generator stator ground fault reoccurs immediately and after the main transformer high-voltage side ground fault is removed, generator stator ground protection can achieve quick action.