RF power amplifier is at the end of the radio transmitter, it provides RF power for receiving antenna. RF amplifier is more energy emission link module, and also is the strongest non-linear module, to improve its efficiency to extend battery life and improve its linearity can be improved data efficiency. Linearity and efficiency of class AB RF power amplifier is good compromise and widely used. X-band GaAs FET power amplifier class AB presents selected work points, and impedance matching method to achieve high efficiency. We discussed the amplifier input loop impedance converting circuit, transistor amplifier circuit and the design ideas of the output circuit impedance conversion circuit. The design is very important in analog signal processing circuit class AB high power amplifier. The simulation and experimental results show that the amplifier is in the range of 9.3GHz similar to 9.4GHz, P1db for 24.5dbm, its gain of 10 dB, and mesh distortion rate is very low.