A target monitoring method, a camera, a controller, and a target monitoring system, where the system includes a first camera and a second camera. An overlapping area exists between fields of view of the first camera and the second camera. The method includes obtaining, location information of a to-be-tracked target in a first monitoring picture when the first camera is used as a current primary monitoring camera, determining, based on the location information of the target in the first monitoring picture, whether a location of the target in the first monitoring picture is in the overlapping area, where the overlapping area is an overlapping range between the fields of view of the first camera and the second camera, and switching, the current primary monitoring camera to the second camera when the location of the target in the first monitoring picture is in the overlapping area.