Abstract: The ridge of conventional waveguide is on long side,compare to the normal rectangular waveguide,ridge waveguide possess several unique characters: larger dominant cutoff wavelength,wider single-mode bandwidth,lower equivalent characteristic impedance.Many letters have discussed it.So far,the double-ridge position on the short side of waveguide has not been discussed and reported.Helmholtz equation finite difference method is analyzed and applied to it.Exact transmission characteristic parameters are obtained.Contrasting result with conventional double-ridge waveguide,it shrinks sing-mode bandwidth,so it is an effective ridge bandpass filter.