A VLF/UHF band power amplifier with low operating frequency and wide bandwidth is designed. In order to meet the index requirements, the design adopts three-stage transistor cascade. Selected crystal after the transistor, the input, output and inter-stage matching networks are designed according to the structure and performance of transistors at each stage. The multi-stage L-shaped matching network is really due to the power amplifier’s output, In the impedance matching circuit, the output impedance matching circuit is realized by multi-stage L-shaped matching network combined with 1:1 coaxial balun impedance matching network. The output impedance of the gain stage transistor and the input impedance of the driver stage transistor are matched to 50Ω respectively, and then the inter-stage matching circuit design between them is realized in cascade. The output impedance of the driver stage transistor and the input impedance of the output stage transistor are directly matched together through the multi-stage L-shaped matching network, and the inter-stage matching circuit design between the driver stage transistor and the output stage transistor is realized. Process a 500kHz~1GHz power amplifier is manufactured. The test results show that the output power can reach more 20W, the gain flatness is better than ±3.0dB, and the working efficiency is about 20%.