Abstract: Based on the three dimensional theory of piezoelectric elasticity,this paper analyzes the bending problem of simply supported thick piezoelectric composite rectangular plate with the method of state formulation. Because no assumption is introduced,the method can be used to analyzc this kind of plate with various thicknesses exactly. An intuitive expression is also obtained for the transfor matrix and the calculation is then simplified. At the end of the paper,numerical examples are given and results are discussed.