An X-band magnetically insulated transmission line oscillator (MILO) is configured and investigated numerically with KARAT code. The design thought is introduced, and the typical simulation results are illustrated and analyzed. In simulation, when the voltage is 520 kV, and the current is 64 kA, the high-power microwave (HPM) of TEM mode is generated with a power of 2.18 GW, a frequency of 9.3 GHz, and a power conversion efficiency of 6.5%.