Abstract: Phononic crystals are conception and acoustic materials appeared ten years ago.This kind of periodical structure can be considered as having the function of filtration,i.e.,the crystal breaks into pass-bands and band-gaps due to Prague scatter when vibration or sound with multiple frequencies is transmitted through it.Propagation of vibration and sound in the band-gap is not allowed.On the contrary,other frequency components can pass the crystal freely.Positions of band-gaps and pass-bands can be engineered by evaluating the acoustic wave equations in the crystals.In addition,existence of the band-gaps is closely associated with the Anderson localization of phonons in inhomogeneous media.The concepts,basic features,development,theoretical methods,and potential applications are discussed.