The present invention discloses a dual-band power amplifier, capable of operating at a first frequency and a different second frequency simultaneously. The dual-band power amplifier comprises a first gain stage; a second power stage; an input matching unit electrically connected between the first gain stage and a signal input port; an inter-stage matching unit electrically connected between the first gain stage and the second power stage and an output matching unit electrically connected between the second power stage and an output signal port. According to the dual-band power amplifier and the design formula of matching circuit of the present invention, the present invention can simplify the circuit structure and is suitable for various dual-band communication systems.