In this paper, reciprocal theorem method( RTM) is generalized to solve the problems for the forced vibration of thick rectangular plates based on the Reissner's theory.The paper derives the dynamic basic solution of thick rectangular plates; and the exact analytical solution of the steady-state responses of thick rectangular plates with three clamped edges and one free edge under harmonic uniformly distributed disturbing forces is found by RTM. It is regarded as a simple, convenient andgeneral method for calculating the steady- state responses of forced vibration of thick rectangular plates.