The paper presents a real-time and reliable communication system for a newly developed hybrid underwater robotic vehicle (HURV). The surface monitoring station of the HURV is linked with the onboard underwater control system by a fine and neutral buoyance fiber, which enables the state monitoring and tele-operation mode of the vehicle based on the industrial Ethernet Modbus/TCP via the fiber-optic communication channel. The detailed implementation procedure of the Modbus/TCP protocol is presented, and the real-time performance of the communication system is analyzed. Finally, the dedicated communication design of the HURV is tested in the tank, and the results of the long-time running test show the satisfactory performance of the communication design of the HURV.