Abstract: Ultrasonic leak testing is a new efficient method for locating leak sources. This paper studies the influence of the test direction angle, the test distance, and other factors. CFD vacuum system model is used to simulate the vacuum system leakage and related parameters are calculated. Experiments for vacuum system leakage and valve inlet leakage were carried out. An ultrasonic leakage testing method is proposed, and the relationship between the sound signal and leakage is found.