Due to imperfect renovation of the unit 4’s controlling and security systems of the Guodian Jiujiang Power Plant, some problems occurred such as the servomotor of medium-high and medium pressure governor steam valve was not sufficient in openness during the static test and the movable test of the main steam valve could not be carried out normally. An analysis was carried out on the causes and practical countermeasures were taken to eliminate the renovation-caused problems, which are proved to be effective.