Aiming at the low precision problem based on empirical formulas, this paper presents a fast and accurate method for computer aided design of the evanescent mode waveguide filter. By establishing an equivalent circuit model of the filter, combining the circuit and the full wave simulation technology, the filter structure sizes can be easily determined through an iterative simulation procedure. This technique avoids time-consuming full wave simulation optimization process. Finally, a sixth order evanescent waveguide filter with dielectric loading is designed. The full wave simulation result shows that the filter frequency response meets the design specifications and verifies the validity of the method.