According to requirements of online steel ball surface defect inspection, the automatic detection method of spherical surface defect on the track has been posed. To ensure photographing of the whole steel ball surface, the six CCD video cameras are used in this system. To overcome steel ball surface reflection, the red LED light source is used, and then the real and clear images are got. The steel ball surface defect is recognized accurately by means of image recognition technology and image reconstruction technology etc. This method provides theoretical basis and technical support for ball defection and quality classification.