The invention relates to the field of optical processing and detecting, in particular to a device and method for controlling medium-frequency errors of an aspherical-surface optical element. The technical problem that medium-frequency errors are hard to restrain in an existing aspherical-surface polishing process is solved. The device comprises a lens clamping unit, a lens rotating shaft, a polishing grinding head, a polishing pad, a cylinder, a grinding head rotating shaft and a grinding head disc unit composed of auxiliary disc sleeves, a screw supporting ring and fixing screws. According to the relative movement mode of the polishing grinding head and a lens to be polished, the polishing grinding head revolves on own axis while the lens to be polished does not move, and the polishing grinding head is not fed in the radial direction of the lens to be polished; or the polishing grinding head and the lens to be polished rotate in opposite directions, and the polishing grinding head is not fed in the radial direction of the lens to be polished. According to the device and method, material removal of the lens to be polished is achieved through the relative movement mode of the polishing grinding head and the lens to be polished, medium-frequency errors of the lens to be polished are eliminated through smoothening, and the smoothening effect is good; the polishing grinding head is convenient to manufacture, the quality of the aspherical-surface optical element is improved, and the performance of an optical system is improved.