The service environment of the high speed gear-box shell is bad, fatigue and tensile damage exist at the same time, the service cycle is long, and the fault damage data is insufficient. Therefore, according to the service characteristics and safety requirements of the high speed gear-box shell, based on the performance degradation method, the acoustic emission technique is used to monitor the damage process of the gear-box shell. A method using the Adaboost algorithm to adjust the distribution of samples is proposed to establish the degradation model, which can characterize the damage state of the gear-box shell. By analyzing the acoustic emission signal of the damage process, the effective fault diagnosis of the box is realized. The absolute error of the tensile damage diagnosis of the shell is less than 30s, and the relative error of fatigue damage diagnosis is less than 1.1{%