Abstract: The strain of surface crack front of cantilever bend loaded sample was controlled by COD displacement gage, the propagation characteristics of low cycle fatigue surface crack of 10CrNiMo structural steel were studied by increasing the strain gradually, and the fracture morphology was observed by scanning electron microscopy. The results show that the surface crack propagation rate had good power ruler relation with the total strain range for crack front. Some tyre-figure appeared near the crack source, serious squeezing happened at the beginning stage of crack propagation, major secondary cracks were found at the middle stage of crack propagation, the fatigue striation was obvious at the late stage of crack propagation, and typical dimples were found on the last fracture area.The crack propagated in sharpening-blunting mechanism and fractured in toughness mode finally.