Abstract: Through the circuit models of bandpass fillter, the main factors of affecting the resonant power are presented: unloaded quality factor Qu, relative bandwidth, main coupling coefficient and cross-coupling. For the effect of relative bandwith and main coupling coefficient, a reasonable explanation with the theory of group delay is given. For the effect of cross-coupling coefficient to some resonators in cascaded-triplet(CT) and cascaded-quadruplet(CQ) sections, a qualitative analysis by phase method is given. Finally, a TM mode ceramic dielectric resonator filters with CT sections is made, the experiment result agrees very well with the circuit simulation one.