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.