There are large demands for concrete apparent inspection of headrace tunnel of hydropower station, the traditional inspection methods has high personal safety risk, the personnel judge the defect information are too subjectively and it is difficult for personnel to reach the inclined shaft section with large slope. For this case, a tethered inspection robot system for headrace tunnel was proposed. The main body of tracked mobile robot was developed by using materials with high friction coefficient, so that the robot has strong environmental adaptability. The defect inspection technology combining three-dimensional laser and multi degree of freedom pan tilt camera was adopted to ensure the accuracy of defect inspection. The tethered power supply and data communication mode of the robot in the tunnel environment was expounded, and a perfect long-distance DC power supply system was designed. Finally, the robot principle prototype was built and demonstrated in the headrace tunnel with a length of 500 m. The test result shows that the robot can replace the manual to complete the inspection task of full coverage apparent defects in the headrace tunnel with complex structure.