Abstract: To raise the accuracy of the fault diagnosis of the gear,through the study on resonance-demodula- tion technology of picking up the shock pulses,and combining“the matrix distinguishing sieve method and“the double characteristic analysis method”,this article concludes the basic diagnosis rules of the wire rolling mill gear box based on analysis of a great deal experimented and tested data,and identification of twenty-one hidden troubles.The rules have been applied in the real fault diagnosis,and are proved to work well.