The invention relates to an ultra-static flywheel with an active disturbance rejection function. The ultra-static flywheel comprises a flywheel body and an active control platform. The active control platform comprises an upper platform, a lower platform and multiple supporting legs connected in parallel. The upper platform and the lower platform are movably connected through the supporting legs connected in parallel. The relative positions of the upper platform and the lower platform are controlled through control over stretching of the supporting legs connected in parallel. The flywheel body is installed on the upper platform of the active control platform through a flywheel installation shaft and rotates around the axis to provide the pose control moment of a spacecraft. The invention further discloses an application method for the ultra-static flywheel with the active disturbance rejection function. The ultra-static flywheel has the beneficial effects that the movably-connected active control platform is adopted, the flywheel body is installed on the active control platform, and the high-frequency disturbance moment of the flywheel body can be subjected to rapid response and accurate compensation, so that the high-accuracy control moment is output, and control is simple.