In this paper it is mainly presented on the corrosion fatigue crack propagation behavior of the ship structural steels such as KA36 (TMCP) and KAS steel in sour crude oil environment, based on the corrosion fatigue crack propagation test results and corrosion fatigue life test results in sour crude oil containing 400 ppm H₂S and in air. The crack propagation rate of these steels in the sour crude oil was accelerated in the stress intensity factor range, Δ K higher than about 16 MPa√ m . The rate of acceleration of the crack propagation rate, da/dN in the sour crude oil in the Δ K of 30 MPa√ m was 7 for KA36 (TMCP) and KAS steel. In higher stress range of S-N curves for the round notched bar specimes of KA36 (TMCP), the influence of sour crude oil containing 400 ppm H₂S on the fatigue life was observed obviously. The fatigue life ratios decreased with decreasing the stress to unity at the lower axial stress of about 200 MPa. It was found that brittle striation appeared predominantly in the accelerated crack propagation area of fracture surfaces in the sour crude oil. The striation spacing per cycle, S obtained from measured striation spacing Δ S versrs Δ K curve was well coincident with the da/dN Δ K curve in the accelerated crack propagation area. It might be concluded that the environmental enhancement of the crack propagation rate in sour crude oil is dependent on hydrogen evolved by reaction between the ship structural steels and hydrogen sulfide in sour crude oil. The further works recommended to study in future are touched in brief.