This paper introduces the design of a power amplifier based on cascode. In order to meet the requirements of high precision, the power amplifier circuit needs to have as little distortion as possible. Hence, class A amplifier is used to minimize the distortion. At the same time, to make the amplification stage have better frequency characteristics and not reduce the input impedance, the cascode is used as the main circuit of the amplification stage. The design has been verified in practical applications and the indicators can meet the requirements.