To clarify the effects of gas and liquid media on the performance of high-speed hydrodynamic seal, the comparison analysis and experimental research on the sealing performance of two phases were carried out. The numerical analysis models of gas and liquid phases in the end face fluid region of hydrodynamic seal were established. The effects of operating parameters such as rotational speed, pressure difference, groove depth, groove number, groove-dam ratio and end face structure parameters on gas and liquid leakage and opening force of hydrodynamic seal were analyzed. The test device of hydrodynamic seal was developed independently, and the tests of variable speed, pressure difference and seal face wear were carried out. The effects of operating parameters such as speed and pressure difference on gas leakage rate, liquid leakage rate and seal face wear rate were obtained. The results of numerical simulation and experiment show that the opening force and leakage of liquid seal are larger than those of gas seal at the same speed and pressure. Under different structural parameters, the opening forces of gas phase and liquid phase seal have maximum values. The optimal structural parameters are different for the gas and liquid phase seal when the opening forces reach maximum values. The optimum ratio of slot to dam and the number of optimal grooves in liquid phase seal are smaller than that in gas seal. The opening speed of liquid seal is lower than those of gas seal, indicating that liquid dynamic pressure seal is easier to open than gas dynamic pressure seal. Seal face wear is serious at low speed and almost no wear at high speed. Hydrodynamic seals are more suitable for high speed conditions.