Abstract: When liquid hydrocarbon pipeline is leaked, the effective prediction of leakage volume and leakage diffusion area is the foundation of shutdown and plugging plan optimization, as well as the reliable guarantee of safe, eco-friendly and economic pipeline operation. In this paper, the status and restriction of the studies on the internal flow and external diffusion in the process of pipeline leakage were investigated, including hydrothermal transient, liquid column separation and seepage diffusion in the soil. And it is shown that the internal flow in the process of pipeline leakage is involved with gas-liquid fast transient process and quasi-stable state slow transient process (such as gas release, cavity flow and liquid column separation), and it is concerned with the problems of flow-heat phase transition coupling and the effects of multiple constraints. Its overall process and mechanism haven't been revealed effectively. On the other hand, the effect of the surrounding conditions outside the leakage section on the conduit flow and the flowing at the leakage section and the seepage diffusion laws of leaked liquid hydrocarbon in the surroundings have not been figured out completely. Then, the global research results of external flow heat transfer and leakage calculation in the process of liquid hydrocarbon pipeline leakage were reviewed and the related experimental studies were analyzed. And finally, it was proposed that its key research and development directions focus on gas-liquid transient flow with the consideration of liquid hydrocarbon phase transition, the flowing characteristic of leaked section, the flow, diffusion and seepage law of leaked liquid hydrocarbon in complicated surroundings, leakage calculation and the optimization of shutdown plan with the minimum leakage volume as the target.