A novel selective stator earth fault protection based on zero-sequence direction element is proposed， which can overcome the shortage of stator earth fault protection applied to generator connected as expanding unit. In the proposed algorithm， the zero-sequence direction criterion is calculated with zero-sequence current of generator terminal， the secondary current of neutral earthing transformer and zero-sequence voltage of generator， and its operating border can be set flexibly. The presented criterion can differentiate between a network earth fault and a generator stator earth fault exactly， which has been realized in digital generator protection. Experiment results show its validity and reliability.