Abstract: Using the symmetry reduction method,elliptical steel cylinders are periodically arrayed in air,which forms the two-dimensional triangular lattice phononic crystal.The band structures are computed by the plane wave expansion (PWE) method.Numerical results show that the degeneracy at high symmetry point of Brillouin zone can be lifted by using elliptical scatters,which lowers the frequency for opening band gaps.Besides,the lower symmetry is,the easier it is to open wide low frequency band gaps.In contrast,the higher it is,the easier it is to open wide high frequency band gaps.These results can be used in industrial design to isolate low frequency noise.