In this paper , the method , which is called Computer Aided Perturbation (CAP) , is used for the optimization design of the multi - stage microwave amplifier circuits. The justified topology structures and required parameters of the circuits are designed automatically by this method , with the aid of the high - speed calculation and logical judgement of the computer. A two - stage microwave amplifier in the band of 2.5GHz - 4.5GHz is designed by use of the compiled design program , and the results are simulated in the microwave circuits CAD software Microwave - Scope , which proves the reliability and utility of the method.