Abstract: Analyses were conducted on the mechanism of stress corrosion and the cause of stress corrosion crack propagation of the steam turbine low-pressure impeller in nuclear power units, and the calculation model for stress corrosion crack propagation life was established combined with Clark model and Pairs model in the corrosion environment. Taking the second and third stage impeller blade root grooves of the low-pressure steam turbine in a nuclear power unit as the research object, the propagation life of stress corrosion crack was researched and analyzed. Results show that the crack propagation life calculated according to the stress corrosion crack propagation rate with the two models can meet the requirement of the service life（60 years） of the serviceable part of the steam turbine in nuclear power units. The crack propagation life from Pairs model is more conservative than that from Clark model, and the safety factor can be selected within 2-3 when estimating the crack propagation life with Clark model, while the change of temperature has a significant influence on the crack propagation rate with Clark model.