Abstract: The gas pipeline leak process is subject to many uncertain factors during its occurrence and progress with a variety of accident forms, therefore, the research of gas pipeline leak process is always an important issue in the technical field of pipeline safety. And the research is very active at home and abroad. Several classic gas diffusion models have been proposed, such as Gaussian model, Sutton model, BM model, FEM3 model etc., which are distinguished by the different stages of leak process and diffusion medium types. The application scope of these models has been given respectively, and their advantages and disadvantages have been compared, too. On this basis, some other popular gas diffusion models which have been proposed in recent years are introduced, such as AFTOX model, HEGADAS model, DEGADIS model, HGSYSTEM model, INPUFF model, SLAB model, etc.. Furthermore, some explosion/flame models are also described, such as the probability density function (PDF) transport equation model, conditional moment closure model, the simplified PDF model, association moment model. According to the requirements of industrial production, the leakage process of gas pipeline has been analyzed, and the classification of study has been explained. The problems in the current study and the future developments of the technical field of pipeline safety have also been pointed out.