In order to provide theoretical reference for the volume design of the terminal sump, this paper analyses the physical process of leakage and evaporation at the LNG terminal using. Combined with the theory of orifice leakage and evaporation diffusion and the actual project scenario, the corresponding mathematical model is given. From qualitative analysis, the main factors affecting LNG leakage and evaporation diffusion are given. The mathematical model is applied to engineering practice, and a large number of calculations are carried out to give the quantitative relationship between leakage, evaporation and diffusion and various influencing factors. Through research, it is found that the leakage of LNG is far greater than the evaporation on the wharf. When designing the volume of the sump, the evaporation of LNG on the wharf can be ignored. According to the leakage model of the pipeline orifice, the credible leakage volume in line with the actual project can be obtained.