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To study the process of the cryogenic propellants during self-pressurization at room temperature, a visual experimental system is designed, which uses the liquid nitrogen as the simulation medium. The change rules of the pressure and temperature as well as the influences of the volume filling rate on the pressure and temperature are analyzed. The experimental results show that the temperature stratification is significant in the gas and liquid regions along ihe axial direction, and the temperature rising rate in the liquid region is lower than the saturation temperature rising rate which is caused by the gas pressure. The pressure rising curve can he divided into three typical sections: the initial section, the transition section and the stabilization section, and ihe pressure rising rate in the stabilization section increases with the volume filling rate. While in the liquid region, the convection is suppressed during the self-pressurization, and the vaporliquid interface is gradually moving into the quasi stationary state. The temperature boundary conditions for the simulation are acquired from the experiment, and the physical process of 175 s during the self-pressurization is simulated by using the volume of fluid (VOF) model. The variation of the pressure curve sirnulated is essentially in agreement with the experimental results, and the pressure rising rate in the stabilization section is about 1. 58 times of the experiment. This paper gives the rule of the tank self-pressurization by the experiment and simulation, which can provide a reference for the cryogenic propellants storage and thermal protection design of tanks. [ABSTRACT FROM AUTHOR]