Abstract: P-a-N curve and P-da/dN-Δk curve for 30CrMnSiNi2A steel are given according to statistical analysis method for metal materials. The test data in different stress ratio conditions are analyzed and compared. Reliability analysis is performed and the mean value da/dN-Δk curve and 99.9% P-da/dN-Δk curve are discussed. The P-da/dN-Δk curve for 30CrMnSiNi2A bears a close relationship with stress ratio. The crack growth rate increases with the stress ratio. The increase tendency is more obvious when higher reliability is demanded.