Abstract: Under cantilever bend loading,surface crack propagation characteristics of 800MPa grade 10CrNiMo structural steel in 3.5% NaCl aqueous solution were studied and the surface crack propagation rate(SCPR) of the steel in such corrosion circumstance was compared with that in air.The results manifest that at the beginning of surface crack growth,SCPR is quicker in 3.5% NaCl aqueous solution than that in air,while as the total strain range increasing,this difference of SCPR becomes less and less,and when the total strain range is near to 1%,the SCPRs are basically equivalent in two different environments.Corrosion fatigue specimen fracture appearance was observed under metallurgical microscope,scanning electric mirror and X-ray energy spectrum equipment and the results indicate at the late stage of surface crack propagation,many corrosion products such as ferrous oxides were found to be accumulated inside the crack,which increase close-effect of surface crack propagation and retard its growth.