Abstract: Waveguide E-plane with metal diaphragm is analyzed by Conservation of Complex Power Technique.The Generalized scattering matrices are calculated.For narrowband design with a low-pass filter prototype,based on a half-wave distributed step-impedance filter prototype,the normalized impedance inverter values are determined.CAD program is developed for the waveguide E-plane filter,several narrowband and wideband band-pass filter are designed,the results agree well with those from HFSS or published.