According to the actual device size, a three-dimensional numerical simulation model of the coaxial magnetically insulated transmission line with a helical inductor is developed. The diode with an appropriate distance between anode and cathode is selected as a load of the transmission line. Setting the device parameters, the device is simulated. Comparing the simulation results with the experimental data, the reliability of the simulation is proved. By combining with the corresponding experimental data, the transmission efficiency of the coaxial magnetically insulated transmission lines with adding the structure of helical inductor is analyzed.