As the fundamental issue of procuratorial power, the qualitative issue of procuratorial power is direct? ly related to the construction of China’s Rule of Law and the development of China’s constitutional government. Under the background of supervision system reform, procuratorial power should be redefined as judicial supervi? sion power which refers to the sublation of the judicial power theory, prosecution power theory, duality theory and legal supervision theory about the nature of procuratorial power. It means that the procuratorial power should be a kind of supervision power in the supervision system which relates to the jurisdiction of the people’s court, the investigation power of the public security organ, the law enforcement power of the administrative organ and the investigation power of the supervision committee. Under the nature of judicial supervision power, the corre? sponding reform of supervision system has not“weakened”, but“strengthened”the procuratorial power.