Abstract: In order to solve the problem of the large parasitism and small bandwidth of GaN high-power amplifiers, this paper proposes a multi-section low-loss output matching network, which expands the working bandwidth, reduces power loss, and achieves the best fundamental impedance and smaller second harmonic impedance. At the same time, a matching network with out-of-band suppression capability is proposed and used for inter-stage and input matching to achieve impedance transformation. The addition of lossy matching at the input end reduces the difficulty of broadband matching and increases the circuit stability. The chip area of the circuit is 4.4 mm×4.0 mm. The post-simulation shows that the relative bandwidth of the working frequency reaches 40%. Within 4 - 6 GHz, the input return loss of the power amplifier is better than −12.8 dB, the output return loss is better than −11.2 dB, the small-signal gain is 28.6±1.2 dB, the saturated output power is 45.6 dBm (36 W), the flatness is ±0.3 dBm, and the power-added efficiency is 43% - 48.9%. It can be widely used in C-band satellite communication, radar and other wireless communication fields.