The utility model discloses a submarine cable maintenance underwater robot system. The system comprises a water surface unit and an underwater unit. The water surface unit comprises a power supply, a water-surface optical transmitter and receiver, a control unit and a display unit. The underwater unit is connected to the water surface unit through an optical-fiber electric power composite cable. The underwater unit comprises an underwater robot carrier, an underwater optical transmitter and receiver, a depthometer, a gyroscopic compass, an underwater TV, a propulsion apparatus, a height gauge, a manipulator apparatus, a sub-bottom profiler, a side scanning sonar device, an image synthesis apparatus and the like. The system of the utility model integrates multiple field technology means, such as the underwater robot, a sonar system, cable detection equipment and the like. A set of working platform possessing a submarine cable underwater maintenance function is established. Under a complex sea environment, safe detection can be performed on the submarine cable and certain maintenance work can be performed. Compared to the prior art, a detection scope and precision are increased and working cost is reduced.