Band pass filters of PBG(photonic band-gap) structures were analyzed based on the transmission line theory in this paper,and a novel K band dual-mode band-pass filter was designed and simulated by using this theoretical analysis.Due to their unique stop bands characteristics and slow-wave effects,PBG structures exhibit good suppression of high order harmonics and reduce geometrical size of circuits system to meet the requirement of miniaturization.A good agreement between the experiment and simulation(with Ansoft's Ensemble software) results had been achieved.The center pass-band frequency of this filter is 25.2 GHz,and insertion loss is less than -4.5dB.Its-3dB band width is 1.8GHz about 7% of center frequency.