The rotary steering drilling system can adjust the deviation and azimuth of the well in real time,so as to control the drilling direction and azimuth of the bit.The dynamic seal in the offset mechanism of the steering drilling system has a great impact on the reliability of the whole system.Combined with the actual working conditions of rotary steering drilling system,the effects of downhole high temperature and high pressure,double side pressure of dynamic seal and stress relaxation of rubber material on seal were considered.The sealing performance of slip ring combined seal was analyzed by using the fluid infiltration loading method in the finite element software.The effects of environmental pressure,downhole temperature and O-ring compression ratio on the contact pressure and Mises stress of the main sealing surface of the combined seal were analyzed.The results show that with the increase of the medium pressure,although the pressure difference between the two sides of the seal remains unchanged,the maximum contact pressure of the seal system is still increasing,and the pressure inside the seal is much larger than that outside the seal.The stress relaxation has a great influence on the performance of the combined seal in the initial stage.The influence of temperature on contact pressure of dynamic seal is less than that of ambient pressure.Higher compression ratio can increase the contact length of the main sealing surface of the combined seal,and reduce the maximum contact pressure to a certain extent,so the wear of the sealing surface can be reduced.