In this paper, we present a 20 GHz low-loss dual-mode channel filter designed by using mode matching method. The performance of dual-mode channel filter mainly depends on iris characteristics. Therefore the exact design of iris is the key point to get good frequncy response of the filter. MOde matching technique is widely used ot design several kinds of waveguide filters because it is simple in theory and can easily calculate the scattering matrices at the discontinuities with simple structure like iris coupled filters. Additionally the effect for finite thickness of the iris in the dual-mode cavity iflter is analyzed by te full-wave method, providing the exact filter implementation without trial and error.