The vibration frequency and displacement shapes of thickness shear vibrations of quartz crystal plate were obtained by establishing three dimensional model of quartz crystal plate and using the finite element software ANSYS. The convergence of numerical results was verified and the selection method of optimal length/thickness of quartz crystal plate was proposed for avoiding strong coupling of vibration modes. The hexahedron mesh was more easily to find the thickness shear vibrations of quartz crystal plate compared with tetrahedron mesh during modeling.