The invention provides a platform border-crossing detection system. The system comprises an even number of cameras with cleaning assemblies, the cameras are arranged above a platform warning line, thedirections of the camera lenses are parallel to the direction of the warning line. The two ends of the warning line are respectively provided with one camera, the other cameras are arranged in pairs,the positions of the camera lenses arranged in pairs are opposite, and the cleaning assemblies are arranged at the outer sides of the cameras. A control chip is arranged on a main control board in each camera, and a border-crossing detection method is arranged in the chip. According to the present invention, the working pressure of the workers on a platform can be reduced, and the safety of the platform is improved. And the cameras are provided with the cleaning devices, so that the shooting definition of the cameras is ensured. The border-crossing detection method in the system not only considers whether the center of gravity of a pedestrian target exceeds the line, but also judges whether the point of the bottom border of the pedestrian target intersects with the border, and eliminatesthe angle error of the camera shooting, and reduces the error that the center of gravity of the pedestrian target exceeds the line in the video image but actually the two feet of the pedestrian targetdo not exceed the line.