A design method of Lx band high Power amplifier is introduced in this paper. The high power amplifier is made up of four power transistors which are connected through power divider and combiner network formed by 3dB couplers and by using the software of ADS, the power amplifier is simulated and optimized. The simulation and test results show that the output power is over than 930W, the PAE more than 43%, the gain greater than 15dB and the flatness less than 0.8dB in the Lx band.