The invention discloses a moving object detection method, device and system. The method includes the steps that first, a background difference image of a difference image is digitalized between an input image and a preset background image; second, the digitalized images of all frames are compared, overlapped areas still serve as an object area, added areas are converted into the target area from a background area, and reduced areas are converted into the background area from the target area; third, one added area, one reduced area and one overlapped area are extracted to be a single integrated area, and moving objects displayed on all the integrated areas can be obtained; fourth, based on the acquired area parameters, the moving objects are detected through calculation. According to the moving object detection method, the moving objects displayed in the integrated areas can be detected, the moving target of each detected object can be independently detected, and the amount of calculation used for moving target detection can be reduced.