Abstract: This paper introduces the design steps and theories of small-signal transistor amplifier,gives an comprehensive description about design procedure of L band small-signal amplifier with ADS software,and the simulating results are made.These results show that this design can meet the required performance of the specified amplifier.This kind of approach,presented by the paper,can design L band LNA and small-signal power amplifier and accelerate exploitation of amplifier product,and it has an important practical value.This kinds of amplifier can be used in microwave relay,digital audio satellite broadcasting,GPS and so on.