Accurate control and rapid regulation of the liquid nitrogen supplying pressure are the basis for the total temperature operation of the cryogenic wind tunnel. The pressure evolution during the discharging process and external pressurization in an accumulator are measured experimentally. The thermal boundary conditions of the tank during the test are mathematically obtained with the consideration of frosting and convective heat transfer. A numerical framework of two-phase flow based on the volume of fluid (VOF) and the heat and mass transfer model is carried out. The computed results with the accommodation coefficient of β = 10−6 in the Lee model are closer to the measured values than using the original value of 0.1, and the laminar model is more suitable for the numerical study of the gas-liquid transfer in the tank than the turbulent model. The growing dynamic process of gas-liquid interface and temperature distribution during the entire test is achieved. Thermal stratification is formed though the coming liquid nitrogen is highly subcooled. The liquid level has not been stable immediately but grows slowly when the pressure reaches the set value. The simulated temperature evolution, distribution, and the final volume fraction of gaseous nitrogen are satisfactorily consistent with the experiments. The results show that the numerical model can simulate the complex heat and mass transfer characteristics inside the cryogenic accumulator and provide theoretical guidance for injection pressure control.