In order to solve the problem of clutch slip caused by excessive pressure loss of rotary joint seal in marine field, a mechanical seal with V-shaped groove in end face which can reduce the pressure loss was proposed. This proposed seal can enhance the sealing performance of rotary joint, ensure the normal operation of rotary joint, and reduce the rotating machinery failure caused by the failure of rotary joint seal. In this research, the numerical model of the flow field of the rotary joint mechanical seal was firstly constructed, and then the accuracy of the model was verified by the pressure loss test bench of the rotary joint. Finally, the V-shaped groove type, micro-pit type and arc-shaped groove type of the rotary joint mechanical seal proposed in this research were compared and analyzed. The results show that compared with the original grooveless rotary joint mechanical seal, the pressure loss of the V-shaped groove type rotary joint mechanical seal can be reduced by about 10 %, the pressure loss of the micro-pit type rotary joint mechanical seal can be increased by about 4 %, and the pressure loss of the arc-shaped groove type rotary joint mechanical seal can be increased by about 21%.