Abstract: The failure reason of input gear in improve system of tower crane was analyzed by means of macroscopic examination, chemical composition analysis, non-metallic inclusions detection, hardness testing, metallographic examination and so on. The results showed that the failure model of input gear was contact fatigue failure, the hardness, wear resistance and fatigue life of material were reduced by the trend of distribution network ferrite, it was the main reason for early failure of input gear. Meanwhile, the preventive measures were recommended.