The operating temperature near the first shaft seal stage was found over the design working temperature of O rings during the hot commission of reactor coolant pumps. And to avoid the influence on safety and reliability of reactor coolant pump due to O rings fast ageing under high temperature, the disassembly of mechanical seal and changing new O tings were carded out according to design opinion. The paper introduces and analyzes the structure and function of reactor coolant pump in detail, and explains the disassembly checking, treatment and re-assembly work. By means of using TQM, it gives an optimized analysis to the whole management progress and keeps disassembly work, treatment work and re-assembly work proceeding in high quality and high efficiency. It also supplies engineering experience for the follow-up reactor coolant pump repair and treatment work on site.