Abstract: In order to explore the transient characteristics of the stall flow signal of the contra-rotating fan, the wavelet analysis method with strong ability to identify the instantaneous characteristics of the flow signal is introduced into the analysis of the stall characteristics of the contra-rotating fan , and a stall diagnosis method combining FFT technique and wavelet-time-frequency analysis is proposed. Firstly, based on the outlet throttle model, numerical simulation and analysis of the 3-D unsteady flow inside the contra-rotating fan under a stall condition is carried out; Secondly, the static pressure signal in the flow field of the fan is processed and analyzed by using the proposed stall diagnosis method. The results show that the contra-rotating fan enters a stall state after 10 rotation period, which occurs with the appearance of leading edge overflow and trailing edge backflow. In addition, the FFT technique determines from the perspective of frequency domain that the stall characteristics are manifested as the appearance of 70Hz and 140Hz frequency components, while the wavelet-time-frequency analysis found that the contra-rotating fan began to appear 70Hz and 140Hz frequency components from the perspective of time-frequency domain at the 10th rotation period. It is proved that the method proposed has a good performance for the diagnosis and analysis of the stall characteristics of the fan.