A synthesis method for a few hundred megawatt level power microwave is presented in this paper. Based on the coupling wave theory and the polarized wave orthogonal theory, the pulse series of one gigawatt level power microwave and one hundred megawatt level power microwave can be put in two separate ports and put out from one common port. The synthesizer is unitized by two cylindrical waveguides which are back to back combined; the cylindrical waveguide which is joined with the output port is named main channel, and the other cylindrical waveguide is called associate channel. The main channel transmits horizontally polarized TE011 mode microwave, and the operation frequency band is only limited to the barrier frequency c. The associate channel transmits vertical polarized TE011 mode microwave, and the operation frequency band can reach up to several hundred mega hertz. High power experiment indicates that the transmission energy efficiency of the main channel is nearly 100% and the coupling energy efficiency of the associate channel is above 87%, the power capacity of the main channel is more than 1GW and that of the associate channel is about 300 MW.