Abstract: This paper reviews the leak testing in the development of the experimental module of the Tiangong-I target spacecraft, including the leak testing items, the leak testing methods and the leak testing results. Stresses are put on the following three methods, namely, the helium mass spectrum with sniffer, the pressure leak testing, and the helium mass spectrum with cumulation in a non-vacuum container. The leak testing results of Tiangong-I's experimental module validate the feasibility and the effectiveness of each method applied in different leak detection items.