We present a photonic crystal,in which each period is made of a few different parts,called photonic crystal with a complicated periodic structure in this paper.We used optical transmission matrix method for numerical investigation.Calculations show that an extra large band gap can exist in this kind of photonic crystal,comparing with photonic crystals with ordinary structures.Multi channel narrow pass band filtering,pass band filtering,and narrow pass band filtering can be obtained respectively in such a photonic crystal under proper operating parameters.This kind of photonic crystal may find applications in wide band reflectors and wide band optical wave guide.It may also find application in utilizing solar energy.