Abstract: An ultra-wideband dual-slot monopulse tracking corrugated horn is studied in the paper. By analyzing the cutoff frequency and voltage maximum position of differential mode，a design strategy that coupling differential mode signal from the dual-slot corrugated horn is proposed. Based on this，an L/S/C-band dual-slot corrugated horn with L-band monopulse tracking ability is designed. It is demonstrated by the theory analysis，simulation and measured results that in L/S/Cband the horn has excellent matching performance and symmetrical radiation pattern. Besides，the L-band differential signal coupled from the corrugated horn is suitable for monopulse tracking task，satisfying all the requirements. The consistency between the measurements and simulations validate the present design methodology.