Abstract: The principle of triple transmission line type pulse compression device is analyzed, and a built-in high resistance spiral with three parallel winding wires is designed to improve power gain and minimize the device. The circuit simulation model and three-dimensional structure electromagnetic field simulation model are established, and the influence of high resistance spiral characteristic parameters on power gain is analyzed. Based on the optimized results, a compact high power subnanosecond pulse compression device is developed. The results show that when the input pulse width is 8 ns and the power is 1 GW, the output pulse is 1.5 ns and the power is 3.7 GW. The power gain is 3.7. After 300 000 times of operation evaluation, there is no flashover and breakdown inside the device, which verifies the reliability of the design.