1. A motion object monitoring system comprising: a time-of-flight (TOF) camera to capture a scene to obtain an image of the scene and distance data between a plurality of points in the scene and the TOF camera; a processor; and a storage device connected to the processor and storing one or more computerized instructions to be executed by the processor, wherein the storage device comprises: a three-dimensional (3D) model module to build a 3D model of the scene according to the image of the scene and the distance data between the plurality of points in the scene and the TOF camera; an information gathering module obtaining specific features of the monitored objects by detecting the built 3D model of the scene, and giving numbers to each of the monitored objects according to the specific features; a storing and comparing module storing one of the given numbers of each of the monitored objects; and a processing module analyzing the given numbers stored in the storing and comparing module.