The frame of general purpose RF power amplifier working in the 2.4 GHz ISM frequency band was introduced. Design of general purse RF power amplifier could be divided into three parts, i.e. design of the detector and comparator, design of the high gain transmit amplifier, and design of the low noise reception amplifier. Test showed that, the power amplifier could reach 21dB transmitreceive gain for the WLAN system whose output power was less than 20 dBm, the power amplifier could satisfy the need of high transmit power and high receive sensitivity in the application of middle-long distance wireless train communication.