This paper has studied the influence of crystal structure on the band gaps of twodimensional piezoelectric phononic crystal (PCs) through calculating the transmission coefficient of PCs. In order to obtain the transmission coefficient of PCs, a model of PCs with interdigital transducer used to excite and receive acoustic wave has been established. The electrical parameters of this model can be worked out through finite element software. Then, the transmission coefficient of PCs can be obtained through combining the P matrix of interdigital transducer and scattering matrix of PCs. As an example, the interdigital transducer and circle hole PCs has produced in the 128°YX Lithium Niobate matrix. Adjusting the lattice constant of rectangular lattice, the tendency of band gaps of PCs in two directions has been observed both in theory and experiment. The result shows that with the increase of lattice constant in y direction, the bad gap in x direction divided into two range and the band gap in x direction gradually narrowed. Thus the band gap in the y direction is sandwiched between the two band gaps in x direction. The experimental result is agreed well with the calculating one.