A power amplifier （PA） with high outputpower based on the GaAs HBT process is proposed. The design adopts the cascade structure of three-stage amplifiers to improve the power gain of the power amplifier.And the RC lossy stabilization network is connected in series at the base of the power transistor to improve the stability and the gain flatness. Active bias is used to improve the output power， efficiency， and linearity performance of large signal output. A power detection circuit is added at the output stage amplifier to obtain a DC voltage signal that varies with the output power. The layout EM simulation results show that： the output frequency range of the PA is 5.1~ 6.5 GHz， and the gain is 33~33.7 dB. Return loss is less than -9.8 dB， the saturated output power is 32.8~ 34.9 dBm， and peak efficiency is 38.7 %~42%. In the case of meeting the wireless LAN standard 802.11ax and the modulation strategy of MCS7， the output power is 20~21 dBm when the EVM reaches -30 dB. The chip area is 1.69 mm×0.73 mm. The test results show that the S-parameter test results and the simulation results show good consistency， and the output power of the PA is 13.6~19.8dBm when it meets the aforementioned wireless local area network standards.