Abstract: The in-orbit leak detection is an important issue for the manned spacecraft cabin．This paper analyzes the method of in-orbit leak acoustic emission and the basic parameters, including the composition and performance of the leak testing system. The characteristics of the acoustic signals from different-aperture leakage sources are obtained based on the spectral analysis, along with the characteristic-analysis by gas leak detection experiments. The experiment results show that the signal from the operating vacuum pump is mainly below 10 kHz; a number of high-frequency acoustic signals are from the leak; the leak acoustic signal parameters are closely related to the leakage aperture. The analysis on the characteristics of acoustic emission signals is of practical significance for the evaluation of the leak detection and the leakage rate in the spacecraft in orbit.