Abstract: In this paper, by using the mode matching and finite element hybrid method(MM/FE Method),the septum polarizer which was used in the antenna system in the airborne nacelle jammer designed by ourselves is studied. Furthermore, a precise analysis model is given. On the basis of the model, we compute the parmeters of the polarizer accurately, and get the plots of the axial ration VS frequency and the VSWR VS frequency, the result demonstrated a good agreement with the test data.