There are three frequently encountered configurations,in the FET design, which are common source, gate and drain circuits. By comparing them carefully and making effective use of FET epitaxial growth, a reversed channel common-drain circuit has been chosen to make the GaAsFET oscillator. Some electrical specifications, were also analyzed systematically, such as characteristic frequency, maximum output power level, single pulse power gain and resonant frequency,etc. Through the processes of production and adiustment, the completed GaAsFET oscillator has met the demands of the project design. Its frequency band was from 4 GHz to 4. 3 GHz and the output power level came up to more than 100 roW. The final oscillator has the features of tiny errors,great stability and a great practical value.