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 system voltage and the bias circuit provides a working voltage according to the system voltage. The output stage circuit receives the working voltage so as to work at an operation bias point. The dynamic bias controlling circuit receives the working voltage and outputs a compensation voltage to the bias circuit according to a variation of the working voltage. When the input power 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 the operation bias point according to the compensation voltage received.