Abstract: Two cases of acoustic emission test on leak were done and the signals characters were analyzed . The results indicated that when the leak mediums were liquid, the acoustic emission signals were continuous signals with low amplitude and the center frequency was about 10~50 kHz; when the leak mediums were gas, the acoustic emission signals were mixed signals with the burst signals being predominant and the center frequency being about 100~400 kHz, and the kind of leaks could be located by Time of Arrival location methods. The research results provided references for similar acoustic emission tests on pressure vessel leak.