According to the basic idea of classical YinYang complementarity and modern dualcomplementarity, in a new, simple and unified way proposed by Luo, the simplified Gurtintype variational principles for elastodynamics of piezoelectric thick plate can be established systematically. The simplified Gurtintype variational principles can fully characterize the initialboundary problem of elastodynamics of piezoelectric thick plate. An important integral relation is given, which can be considered as the generalized principle of virtual work for dynamics of piezoelectric thick plate. Based on this relation, it is possible not only to obtain the principles of virtual work, but also to derive systematically the complementary functionals for eightfield, sixfield, fourfield simplified Gurtintype variational principles and the potential energy functional for threefield and twofield simplified Gurtintype principle for elastodynamics of piezoelectric thick plate by the generalized Legendre transformation given in this paper .Furthermore , with this approach, the intrinsic relation among various principles can be explained clearly.