An integral equation approach is presented to deal with the problems of discontinuity in rectangular waveguides. The integral equations take the modified Green Functions of the waveguide as kernel for the problems which is uniform along E-plane

and the kernel of integral equations is deduced from the Fourier Expansion of the iris surface fields for the problems which is uniform along the H-plane. A group of typical conductor obstcles in the rectangular waveguides have been treated as examples

shewing the approach presented is quite promising for engineering calculations.