The rotary combination sealing composed of Newtonian magnetic fluid and magnetic grease was designed for a high-power motor of certain equipment. The pressure and friction-power formulae of the rotary combination sealing were deduced theoretically. It is shown that the pressure capacity is mainly related with the sealing stage, magnetic field strength, magnetic fluid saturation magnetization and yield stress of magnetic grease, the viscous dissipation power of magnetic grease sealing is approximate proportional to the (2n+1) power of rotational speed(n is the flow index of magnetic grease). A large gap rotary sealing structure that is suitable for high-power motor was designed, and the pressure capacity and temperature change experiments were made in the experimental stage. The experiments prove that theoretical analysis is correct and using the combination sealing of magnetic fluid and magnetic grease in the high-power motor is feasible.