Two photoelectric circuit sets each have a light source, two light switches, optical fibers, photoelectric sensor and computer. The light source emits visible light to the first switch, which is continuously deflected and reflected by a torsional micro-mirror. The light respectively irradiates each of the optical fibers in a composite material optical fiber prepreg layer. If the material is normal, the optical fiber is not damaged, the visible light passes through the optical fiber and irradiates the second switch, and is continuously deflected and reflected by a second torsional micro-mirror, the light irradiates the photoelectric sensor. The sensor outputs an electric signal to the computer. If the material is damaged, the optical fiber here is damaged, another corresponding optical fiber path at an intersection point is also damaged without electric signal output. The computer gives breaking position coordinates at the intersection point of two paths of optical fiber arrays.