Abstract: This paper proposes a method of non-contact ultrasonic leak detection, and builds a system of ultrasonic leak testing based on the principle of gas leak ultrasonic generation and the relation between the sound level and the leakage. An algorithm is developed for the leak testing and several experimental tests are carried out. It is shown that this method can determine whether a leak event occurs and give a leakage amount approximately, which may provide a reference for on-orbit leak detection of the sealed cabin of China's space station.