Abstract: Objectives Electromagnetic waves in long-wave band have significant application value in deep-sea communication and detection. In order to solve the problems of large antenna size, difficult engineering construction and high input power faced by constructing high-power long-wave transmitting system, it is necessary to make full use of the existing infrastructure resources to design a novel one. Methods Firstly, compare the similarities and differences between the horizontal antennas and overhead power lines in the power grid, and conclude the overhead power line can be used as a horizontal antenna. Then, the transmitting system scheme composed of AC overhead power line that is delivering electrical energy, transmitting module, coupling module and separation module is presented, and the design method of each module is proposed. Results A transmitting system of 300kW working at 210Hz based on a 110kV AC power line has been simulated to demonstrate the AC power line can transmit simultaneously electric power and long-wave signals through coupling and separation modules. Electromagnetic simulation results demonstrate that the transmitting system is capable of generating a magnetic field on the order of femtotesla at a distance of 350 km and a depth of 100 meters below the sea surface, thereby meeting the requirements for deep-sea communication. Furthermore, experimental simulations were conducted on a long-wave transmitting system with a transmission power of 20 W, validating the communication capabilities of the proposed method. Conclusions The in-service AC power lines covering the whole country can provide strong support in constructing military and civilian flexible long-wave transmitting system.