Abstract: The pressure and flow rate are calculated for the leaking long-distance pipelines. It is noticed that the variation of the hydraulic parameters in case of the leakage is different from those caused by the valves opened and closed at inlet and outlet. According to the observed variation of the hydraulic parameters with leakage, a model is established for recognizing the abrupt changes of parameters. Based on this model a new leakage monitoring method is presented in which the expanded sequential probability test is applied. Experimental results show that this method can effectively detect the leakage of pipelines.