Abstract: The expressions and characters of some special parameters,such as low frequency cut-off point,critical condition between fast-wave and slow-wave,balanced hybrid condition,high frequency cut-off condition and short circuit condition, are described using the basic theory of corrugated horn.Based on the analysis of the differential mode critical cut-off point of corrugated horn,the coupling aperture positions are correctly chosen by finding the corresponding antinodes of current or voltage.To reduce the reflection of the differential mode,the matching between HE₂₁ mode in corrugated horn and TE₁₀ mode in rectangle waveguide and the matching between coupling aperture and rectangle waveguide are considered,and the dimensions of rectangle waveguide and coupling aperture are then chosen accordingly. A model of C-band differential mode coupling corrugated horn is built and simulated using the Ansoft software.It indicates that the results of the simulation and test agree well with theory analysis,therefore,the proposed C-band differential mode coupling corrugated horn can be applied in realistic engineering.