Abstract: Based on Paris's model of fatigue crack propagation, a fiting formula for the course of fatigue crack growth of 10 Ni5 CrMoV steel and its welded joint was set up, and a statistical analysis on parameters c and m of the formula and fatigue crack growth life was carried out. The results showed that the parameters c and m were in good agreement with fatigue life data, the data of lg c and m complied with normal distribution and had great linear independence, and the fatigue crack growth life was a weibull distribution.