A high power gain microwave amplifier is expected in the equipment to amplify the small signal. The designation idea and procedure of the amplifier whose power gain more than 100dB are discussed in the thesis. It is about the choice of electronic components, the design of circuits, the layout of PCB of the preamplifier, the intermediate amplifier, the terminal amplifier, etc. Finally, the result of the real amplifier shows that the amplifier has met the requirement of the designation. The amplifier is actually used in the recently implementation of a transmission monitoring equipment.