Abstract: In order to investigate the pressure control performance of thermodynamic vent system for orbital cryogenic tanks， the CFD method is adopted to simulate the spray process of the subcooled liquid into liquid hydrogen tank under microgravity. Different injection regions， injection fluxes， injection velocities are comparatively calculated and the effects of these factors on physical field distributions and pressure variation are analyzed. The results show： under lower fluxes and velocities， the inlet liquid could not generate jet flow during gas region injection and will accumulate around the spray inlet， which decreases the pressure control efficiency. Meanwhile， the liquid region injection almost has no impact on the tank pressure control under lower fluxes. The effect of spray pressure control increases as the injection flux and velocity for both gas region and liquid region injections. Under lower fluxes， the gas-liquid-region injection process could be regarded as the superposition of separated gas region and liquid region injection processes. As flux increases， this additivity becomes inapplicable since the interaction between the disturbed flow in gas and liquid regions. The gas-liquid-region injection has the best pressure control performance while the liquid region injection has the worst performance.