Abstract: The paper analyzed the factors influencing the bubble detection rate in ultrasonic leak detection for fuel tank, studied the characteristics of ultrasonic reflection field of transducer, and proposed a new 8-channel parallel cyclic scanning detection mode, maximizing the repetition frequency of each transducer. Then comparative experiment tests were conducted between our 8-channel parallel ultrasonic leak detector and the traditional one. The results showed that, compared to single-channel scanning mode, the multi-channel parallel testing method had much higher detection rates when the single air bubble or long time interval bubbles needed to be detected. So this method was more effective to detect smaller tank leakage (μm diameter).