Abstract: This paper reports the equivalent circuit and the electromechanical coupling factor of the radially polarized thin piezoelectric cylinders. The equivalent circuit is the four-terminal network. Using electroelastic short-circuit modes of vibration and piezoelectric equations, the internal energy of transducer is obtained. The parameters and the equations of the equivalent circuit are obtained with linear equations and internal energy of transducer. The procedure to derive equivalent circuit is applicable to other transducers. Using electromechanical coupling energy, elastic energy and dielectric energy, the electromechanical coupling factor of the transducer is obtained.