The invention discloses a dual-band high-efficiency power amplifier based on a multi-step branch matching network. The dual-band high-efficiency power amplifier comprises an input matching circuit (40), an output matching circuit (50) and a transistor (30). The input matching circuit (40) consists of a first group of microstrip lines which are connected in series with each other, is used for inputting the radio frequency signals and optimizing the transmission of the radio frequency signals at the input end, and is connected with a grid electrode (31) of the transistor (30) in series; and theoutput matching circuit (50) consists of a second group of microstrip lines which are connected with each other in series, is used for outputting the radio frequency signal and optimizing the transmission of the radio frequency signal at the output end, and is connected with the drain electrode (32) of the transistor (30) in series. Based on the principle of a traditional double-frequency impedance converter, a multi-section microstrip line cascade structure is adopted, and the secondary harmonics are controlled while fundamental frequency matching is achieved. The power amplifier can work intwo frequency bands, is large in bandwidth and simple in structure, and achieves the double-frequency high-efficiency performance.