Abstract: In order to ensure the sealing and safety of the manned spacecraft in-orbit for a long time, the in-orbit ultrasonic leak detection technology is studied. this paper focuses on the generation mechanism and spectrum characteristics analysis of gas leakage ultrasound, establishes the relationship between leakage and ultrasonic characteristic quantity, studies the analysis method of leakage ultrasonic signal and implementation strategy in-orbit, and proposes the fast leakage location method in-orbit, then verifies the effectiveness of the method through leakage location test. This study can quickly and accurately determine the location of the leakage point, and solves the problem that existing technology in China cannot accurately locate the leakage point of spacecraft, achieves the goal of quickly and accurately determining the location of leakage point and taking remedial measures.The research can ensuare the continuous safe operation of manned spacecraft in-orbit.