In order to solve the problem of seal failure caused by low useful life and low reliability of rotary seals under the combined effects of bad lubrication, weak corrosive medium, high speed, high pressure conditions, a new type of rotary seal was innovatively proposed in this research. The sealing lip was made of modified polytetrafluoroethylene (PTFE), but it was softer than ordinary modified PTFE, which could significantly reduce the sealing temperature without increasing the friction torque. A rotary seal temperature and torque test bench was designed and built, and the temperature and friction torque characteristics of the seal were studied experimentally. The temperature and friction torque of lip seal and modified PTFE rotary seal at different speeds were compared. The test results show that compared with the lip seal, when the lubrication is bad, the temperature of the modified PTFE rotary seal is reduced by about 3.58 °C, and the friction torque at the same speed is reduced by about 0.005 N·m. When the corrosive medium is weak, the temperature of the modified PTFE rotary seal is reduced by about 0.89 °C, and the friction torque at the same speed is reduced by about 0.015 N·m. Due to the certain pressure of the weak corrosive medium, compared with the bad lubrication, the friction torque of the modified PTFE rotary seal and the lip seal increases by about 0.045 N·m when the corrosive medium is weak. It can be seen that the modified PTFE rotary seal proposed in this research can ensure the normal operation of the rotary seal, thus providing technical support for reducing the rotary mechanical failure caused by the failure of the rotary seal.