The present invention relates to the field of motor detection, and in particular, to an apparatus for detecting an angular displacement, a system for controlling a rotation angle of a motor, a gimbal, and an aircraft. The apparatus for detecting the angular displacement provided the present invention includes a combined magnet, a Hall sensor, and a transmission component. The combined magnet includes a first magnet, a weak magnetic layer, and a second magnet that are sequentially stacked. Magnetic pole directions of the first magnet and the second magnet are opposite and parallel to the weak magnetic layer. The transmission component is connected to the combined magnet, and drives the combined magnet to rotate, or, the transmission component is connected to the Hall sensor, and drives the Hall sensor to rotate. the apparatus for detecting an angular displacement provided the present invention two magnets are combined together to form a combined magnet whose magnetic poles intersect each other to increase magnetic field strength at two poles of the magnet and reduce magnetic field diffusion, so that the apparatus for detecting an angular displacement provided the present invention can reduce interference to surrounding signals from magnetic field.