The invention relates to a generator stator grounding protection system and a parameter measuring method. The method, by using the current and voltage measuring functions of an existing generator stator grounding protection system, performs iterations on the parameter solutions of the leakage impedance equivalent circuit and the excitation impedance equivalent circuit of a grounding transformer soas to finally obtain the final leakage impedance value and the final excitation impedance value of the grounding transformer. The method has a low implement threshold, does not put higher requirements on the original protection platform, can be implemented on the original protection device platform, does not require additional equipment, and automatically tests a primary equipment system parameter required by 20Hz stator grounding protection by a protection device. The method is simple in implement principle, can accurately measure the primary equipment system parameter required by 20 Hz stator grounding protection in real time, obtains an accurate system parameter, and has a promotion value.