Abstract: By means of macroscopic examination, fracture analysis, chemical composition analysis, metallographic examination, hardness testing and so on, the fracture reason of 42CrMo steel excavator pin was analyzed. The results showed that the pin fracture mode was biaxial bending fatigue fracture. There was the brittle white layer ε phase on the pin surface, and the brittleness of the pin surface increased by the serious loose on the white layer, the microcracks on the pin surface led to the fatigue crack initiation. The fatigue resistance of pin reduced by the low nitrided layer depth and hardness of pin, that accelerated the fatigue crack extension, and the early fatigue fracture of pin happened at last.