Abstract: In order to further effectively detect and analyze the defects of the diversion tunnel, this paper uses a robot equipped with a threedimensional laser scanner to carry out the apparent inspection of the lining in the tunnel emptying state. It introduces the operation flow of 3D laser scanning in tunnel inspection, and analyzes the defect statistics and distribution law based on the inspection data. The results show that the three-dimensional laser scanning technology can effectively reflect the apparent cracks of the tunnel, which shows the reliability of the hidden danger detection of the diversion tunnel. The defects of diversion tunnel include cracks and leakage, which are mainly distributed in the upper and lower sections. From the tunnel section, the defects are mainly distributed at the top of the tunnel. Compared with other defects, the crack is the main defect type of the headrace tunnel, so more attention should be paid to the crack propagation at the top of the headrace tunnel during the later project operation and safety inspection.