This paper analyzes the influences of shaft voltage absorbing circuit and brush touching resistance on the performance of generator rotor earth fault protection. Some countermeasures and advices are presented. Prolonging period of electric switches and injected square voltage is suggested to eliminate the influence of shaft voltage. It is necessary for rotor earth fault protection to keep goodtouching of grounding brush and rotor shaft. Rotor earth fault protection configuration of revolving excitation generator is investigated subsequently

and periodical detecting mode is commended.