A 2D phononic crystal (PC) with a sandwich type of heterostructure is proposed by replacing two columns of circular scatter cylinders with two columns of square scatter cylinders. The sonic waveguide characteristics of the structure are calculated from fd= 0 to fd =0.5 by combining the plane-wave expansion method and a supercell technique. The results show that there are defect bands when -45°<θ<45°, f=0.7 and fd = 0.5. The number and position of defect bands change with θ and are symmetric to the direction of (0, 1). For the situation that f= 0.7 and the projection of the diagonal of the square scatter cylinder in the direction of (1, 0) is smaller than 2.118 R, there are defect bands and the number of bands decreases with the increase of fd. The sonic waveguide characteristics of the PC would not change with the orientation and the type of cross-section of the defect cylinders when fd is very small.