Abstract: The application of leaky coaxial cable is becoming more and more widely, and the numerical radiationcharacteristics are paid more and more attention. In the cylindrical coordinate, the propagation path of electromagnetic wavein round tunnel is analyzes based on the radiation theory of leaky coaxial cable, and the radiation field of leaky coaxial cablein round tunnel is simulated by using finite difference time domain(FDTD) and ray tracing method. The process ofcalculation is more concise, and the results are more accurate. The results show that the leaky coaxial cable can cover theshortages of traditional antennas in blind or semi-blind zone, and the duplex communication between inside and outside ofthe tunnel can be realized easily.