In recent years, with the full use of 5G base stations, higher performance of the S-band power amplifier has been required. In order to meet the needs of high gain, high efficiency, wide bandwidth, large power, miniaturization and so on, this paper designs a radio frequency power amplifier worked at 3. 4~ 3. 6 GHz with the parallel open circuit microstrip method based on the step matching circuit. The design method proposed in this paper aims to solve the difficulty of accurate measurement to the dynamic impedance of transistor and the non-negligible difference between theory simulation and practical testing. In this design, the input and output matching network always remain in a dynamic matching condition by utilizing the parallel open circuit microstrip with the adjustable physical length and width. This kind design is beneficial for the later debugging circuit to reach the best matching state. In order to verify the feasibility of the design scheme, this paper designs a radio frequency power amplifier operating at 3. 5 GHz with CREE CGHV40030 and completes circuit implementation and test. The simulation and test results demonstrate that it’ s easy to debug circuit, determine the optimum matching network, realize the test results very closed to the simulation results and obtain good performance by utilizing the proposed design method. The AM-AM distortion is less than 1, the AM-PM distortion is less than 5°/ dB, S11 is less than -5. 1 dB, S12 is larger than 18. 3 dB, the output power is larger than 45 dB, the gain is larger than 12 dBm, and the drain efficiency is larger than 66%.