The invention discloses a detection method for searching a power grid side fault generator stator ground protection maloperation reason. When generator stator ground protection 3U0 acts and causes unit power failure, under the conditions that generator stator insulation is normal and generator stator high-voltage holding test is normal, detected stator voltage 3U0>Uzd and the stator voltage 3U0>t>tzd, wherein t is the time of the Uzd, whether reinforced excitation happens in a generator is detected and whether ground capacitance XC of the generator and a neutral point reactance value XL are basically equal is detected, and if all the four conditions are met at the same time, the reason for protection action can be determined. Therefore, effective measures can be taken, and faults can be prevented from happening again.