Abstract: Due to the existence of high-frequency parasitic parameters in power electronic circuits, high-frequency oscillation occurs during the transient switching process of power devices, resulting in common-mode electromagnetic interference in power converters. This interference affects sensitive components in the system and reduces the reliability and overall efficiency of power converter. This paper analyzes the electromagnetic interference of a gallium nitride buck converter, establishes an equivalent circuit model of the buck converter, and obtains the functional relationship between the switching oscillation of gallium nitride power devices and parasitic parameters. Then, an optimized design method for electromagnetic compatibility of gallium nitride power converters based on ANSYS is proposed. A joint circuit simulation model is established to analyze the impact of parasitic parameters on the switching oscillation of gallium nitride power devices before and after the optimization of PCB board of the buck converter. Finally, the suppression effect of the switching oscillation of gallium nitride power devices is verified through experiments.