Abstract: In order to realize the analysis of microwave devices effected by high power microwave, we mainly studied the semiconductor devices with different scales and waveguide devices. Based on the spectral element method time domain (SETD) method owning spectral accuracy, we have performed the investigations of electro-thermal coupling analysis for semiconductor devices from the micron scale to the nano scale and the analysis for the gas discharge and its inhibition mechanism under the high power microwave environment. Finally, we obtained the variation law of electrical and thermal parameters inside the semiconductor devices effected by electromagnetic signals and gas discharge and its inhibition mechanism inside the microwave devices under the high power microwave environment. The related effect mechanism provids a theoretical guidance for the device design in the complex electromagnetic environment.