Abstract: During the pressurized discharge process of propellant tanks in cryogenic rockets, the effects of high-speed pressurized gas on the liquid surface have the potential to result in issues of significant propellant loss and pressurization failure. To investigate the mechanisms of liquid surface breakage and liquid splashing by such gas flow attack, this study developed a three-dimensional simulation model of pressurized gas injection into a liquid hydrogen tank under high-filling-ratio conditions. The shell conduction model was utilized as a replacement solution for solid wall meshes to effectively describe the fluid-solid heat transfer. The present study primarily compares and analyzes the attack intensity of gas flow and the pressurization performance under different diffuser structures including horizontal-outlet, hemispherical-outlet, and vertical-outlet. The results suggest that the vertical diffuser prompts high-speed pressurized gas flow to exert violent attack on the liquid surface, consequently leading to propellant splashing and intermittent contact between the liquid and the ullage wall. This phenomenon significantly exacerbates evaporation losses of the liquid propellant. Moreover, liquid phase splashing causes an enhancement in gas-liquid heat transfer rate, leading to a decline in ullage temperature. This ultimately results in the pressure of the tank ullage to decrease rather than increase, and in severe cases, it may cause the issue of pressurization failure. In the context of the energy composition during pressurization process, merely 18% to 41% of the input energy is utilized for ullage pressurization, with the residual amount being absorbed by the liquid phase. The energy input to the tank includes the energy carried by the pressurization gas and the heat exchange between the ullage and the wall. The heat transfer from the wall to the ullage is beneficial to pressurization, accounting for 9% to 28% of the total energy input.