Abstract: In this paper, a square metal pole bandpass filter is designed based on the mode matching method. Then the square metal poles are replaced by cylindrical metal poles by using the empirical formula. This kind of filter has a simple structure and can be easily fabricated. So it is very suitable for quantity production. The calculated results are found to be in very good agreement with the experimental data, thus proves the precision of the mode matching method and the validity of the empirical formula.