The leakage of gravity flow drainage pipeline will bring many adverse consequences. But, due to the particularity of gravity flow drainage pipeline, many existing pipeline leakage detection methods are difficult to be applied. To solve this problem, this article proposes a detection method based on the geo-electrical current, which uses leakage holes to connect the inside and outside of the pipeline, and determines the leakage by measuring the current between the electrode moving in the pipeline and the electrode fixed on the ground. The basic working principle of the method is described in this article, and the detection system is designed based on the method above, and the experimental platform is established to test the detection effectiveness of the proposed method. When detecting a 10 m long buried pipeline, the maximum location error is about 0. 4 m, which indicate that this detection system can accurately locate the leakage location, and with better probe positioning method, the error will be futher reduced. According to the measured spike current value, 9 circular leakage holes with the diameter gradient of 0. 5 mm can be clearly distinguished. Nine groups of measured data are used to train the neural network, the mapping relationship between the spike current value and the leakage hole size is roughly obtained, which shows that the leakage hole size can be roughly estimated according to the detection results.