Abstract: Flow parameters of pipelines with gas-liquid two-phase flow are so complicated that the operational parameters inside the pipelines will change in the case of pipeline leakage, and consequently leakage detection difficulty is increased greatly. Based on the basic conservation equations of fluid mechanics, a mathematical model for leakage system with gasliquid two-phase flow was established by using two-fluid model. Then, the leakage laws of pipelines with gas-liquid twophase flow in the flow patterns of stratified flow and slug flow were simulated and analyzed with a 5 km pipeline with gasliquid two-phase flow as the model. And finally, the effects of flow pattern, leakage port size and leakage location on flowing parameters were investigated. It is shown that in the case of pipeline leakage, pressure along the pipeline decreases; the flow rate increases slightly in the upstream of the leakage point while decreasing significantly in the downstream; and the liquid holdup remains nearly unchanged in the upstream while decreasing in the downstream. In the pattern of stratified flow, leakage has no effect on the flow pattern. In the pattern of slug flow, it can be turned into stratified flow in the case of larger leakage and kept unchanged in the case of smaller leakage. The closer the leakage point is to the outlet of pipeline, the smaller the pressure drop amplitude in the upstream of leakage point is.