Abstract: In recent years, the environmental assisted fatigue (EAF) of metal parts in light water reactor has always been a major concern in domestic and international nuclear safety equipment research and regulation. In this paper, the corresponding experimental research data of Japan and U.S. were analyzed in-depth, and the conservative of the F_en calculation result of different metal materials and the sensitivity of the key influence factor were summarized as well. And in combination with domestic actual situation, an assessment method of performing environmental impact fatigue during the process of metal fatigue monitoring in the nuclear power plant was provided with using the F_en correction formula. The result shows that the estimation of environmental impact factor can be carried out at the moment based on the monitoring real transient data in the nuclear power plant with using the F_en correction formula. For the same type of metal materials, the calculation results of fitted F_en formula are very close under different test environments, but the EAF issue in the process of fatigue life assessment of metal parts is not negligible.