Abstract: Pipeline is a major way to transport oil and gas, and its leakage due to failure may lead to disastrous consequences. Therefore, it is essential to early find and immediately treat this hazard and pay high attention to the safety of pipeline operation. In this paper, the principles and classification of leak detecting technologies for oil pipeline are described. The leak detecting technologies, which are all realized by detecting the environment outside the pipeline or the variation of fluid parameters in the pipeline, include flowrate balance method, real-time transient model, statistical analysis, and sonic/negative pressure wave method. Furthermore, the performance of pipeline leak detection system in China and abroad in recent years is investigated, and its application in a leak accident of a Chinese pipeline operating company is discussed. Finally, it is proposed that the combination of flowrate balance method and negative pressure wave method based on ultrasonic flowmeter is most practical for leak detection of current long-distance oil pipelines.