Combining the constitutive equation of piezoelectric ceramic with elastic-dynamical equations and coupling theory of FEM, the finite element control equation for piezoelectric actuator is established. Detailed calculation of the electro-mechanical coupling field parameters is made by the SP1 type longitudinal-bending vibrator and results show it can be used for the transparent calculation for piezoelectric intellectual structure and avoid the black box operation in FEM software. The model lays the foundation to develop the special program for piezoelectric actuator and to study the non-linear constitutive equation of piezoelectric ceramic driven by high-power.