Abstract: This article introduces a design method of GaN power device modulation circuit, which is widely used in high power GaN power amplifier of transmitting chain in the design of T/ R module. It has high voltage operation, large current supply, peak voltage suppression and other functions. The article focuses on the principle of the modulation circuit, of which the peak voltage suppression function is the difficulty of its realization. Through simulation analysis, the key indicators of time delay within 500 ns and negative voltage detection level between -4. 2 V and -3. 8 V are realized. Finally, a PTFE printed board is selected to design the GaN power device modulation circuit and the actual test is consistent with the simulation conclusion from the application of T/ R module. The modulation circuit is small, and it has high reliability. It can be applied to the design of high power GaN power amplifiers, which would have broad application prospects.