Once a hazardous gas leaks, it will pose a serious threat to the safety of people's lives and property. This paper aims to investigate the flow characteristics of heavy gas leakage and diffusion to deal with sudden accidents caused by hazardous gas leakage.First, an experimental platform for the leakage and diffusion of heavy gas is built, and the tracer technique is adopted to visualize the experimental phenomena during the process of gas leakage and diffusion. Second, a computational fluid dynamics (CFD) model is built based on the experimental platform to simulate and analyze the gas leakage and diffusion process. The CFD model is verified by comparing the numerical results with those of experiments using an authoritative evaluation standard procedure. The comparison shows that the related statistical performance measures are all reasonable. Third, a three-dimensional numerical model of a real tank farm is created in full scale and the heavy gas (liquefied petroleum gas) leakage process is simulated and analyzed considering also the effect of wind. Experimental and numerical resultsshow that the heavy gas leakage and diffusion process can be divided into three stages: gas concentration rising stage, gravity sedimentation stage, and gas passive diffusion stage, in which different flow phenomena are observed with different flow characteristics for each of the stages. The phenomena observed in experiment are further analyzed and clarified using fluid dynamics by numerical simulation. The fullscale modeling and simulation of the real tank farm is helpful for taking possible measures once a gas leakage occurs.