A method is proposed to analyze the forced vibration of jack-up rig using a model made by replacing its legs and platform with equivalent beams and a rigid body, respectively, and connecting them by equivalent springs. The exciting forces by waves and currents are calculated by replacing legs with hydrodynamically equivalent cylinders. The transfer matrix method is applied to analyze the dynamic response of the above mentioned model. The accuracy of this method is studied by comparing the results calculated by this method with tank test results by 1/45 scale model, then it has become clear that the method in this paper gives a practically sufficient results.