Abstract: Based on the analysis of gear pump structure and capability, the wavelet transform method is proposed to detect the fault information in the pressure signal from the outlet port of the pump. According to simulation, the third level wavelet coefficients decomposed from the pressure signal in fault state are significantly different from those in normal state and can be used to effectively diagnose whether the working state of gear pump is normal or not. The results show that the wavelet transform is a practical method for fault analysis of gear pump.