A radio frequency (RF) power amplifier is disclosed. The RF power amplifier includes a bias circuit, an output stage circuit and dynamic bias controlling circuit. The bias circuit receives a first system voltage and provides a working voltage accordingly. The output stage circuit receives the working voltage so as to work at an operation bias point. The dynamic bias controlling circuit detects a RF input signal and outputs a compensation voltage to the bias circuit according to variation of the RF input signal, wherein the dynamic bias controlling circuit is an open loop configuration. When an input power of the RF input signal increases and makes the working voltage decreases so as to shift the operation bias point, the bias circuit adjusts the working voltage upward so as to recover or enhance the operation bias point according to the compensation voltage received.