Abstract: In order to study the pressure increase in the tank and the thermal stratification of the cryogenic propellant liquid phase caused by heat leakage in the cryogenic propellant tank, the User-Defined Functions(UDF) were used to explain the variables such as the energy source term, the mass source term of the gas-liquid phase and the phase change saturation temperature in the cryogenic tank. Combined with the VOF model and the cryogenic working fluid material model established by Fluent software, the simulation of the self-pressurization process in the cryogenic liquid nitrogen and liquid krypton tank was realized. The influence of different gas model and liquid phase density model combinations on the selfboosting prediction curve is analyzed. Comparing the experimental and theoretical values of the simulation, it is found that the pressure value obtained by using the actual gas model(Redlich-Kwong-Soave model, R-K-S model) and the Boussinesq approximate liquid phase density model is closer to the theoretical pressure value. In addition, the experimental conditions of different gravity environments and different filling rates were simulated, and the influence of ambient gravity and filling rate on the self-pressurization process of cryogenic liquid krypton tanks was obtained.