Abstract: In this paper, a GaN broadband Doherty power amplifier is designed. A broadband power amplifier of 3.3~3.9 GHz based on CGH40025 chip model is designed, with modeling and electromagnetic field simulation of micro-strip in ADS (Advanced Design system).Using random optimization and gradient optimization method in the ADS with the principle of double impedance matching. The simulation result show that the broadband power amplifier module have a good performance in the wide band of 3.3~3.9 GHz, the gain is 12-13 dB, the maximum output power is 47.7 dBm, and the efficiency is above 65%, the power is back 6dB, the output power is 41.7dBm, and the efficiency is above 47%.The design method can be applied to the broadband radio frequency communication system.