Abstract: In response to the problem that the distance between the coupling coils increases and the coupling degree decreases after the primary coil in wireless charging system is embedded into the pavement structure, the coil structure was optimized to realize the wireless transmission of energy over large distances. The inner diameter, outer diameter and number of turns of the coil were optimized by electromagnetic finite element simulation, and the optimization process of the coil structure parameters with the coupling coefficient as the optimization target was proposed. Meanwhile, the circuit simulation platform of the wireless charging system was built in Simulink, and the performance of the wireless charging system with the optimized coil structure was tested. Results show that with the increase of coil diameter, the coupling coefficient first increases to the peak and then decreases rapidly, and the coupling coefficient gradually increases as the outer diameter of the coil increases. The optimal number of turns of the coil is 9 turns for different outer diameters. Among the three coil parameters, increasing the outside diameter is the most effective way to increase the coil coupling degree. The final optimized parameters of the coil are the outer diameter of 480 mm, the inner diameter of 210 mm, and the number of turns of 9, which can achieve the power transmission at a distance of 300 mm. The output power of the system is maintained between 2.96 kW and 3.70 kW, and the transmission efficiency reaches 86.54%. Besides, the allowable lateral offset distance of the coil is up to 60 mm.