A new three-dimensional (3D) model of a high-power composite ultrasonic transducer is proposed and evaluated in this paper. This transducer comprises two active layers, each with at least two mechanically series-connected piezoelectric elements. A metal mass element is clamped between active layers with two bolts to create a sandwich structure comprising back and front metal radiation masses. The electromechanical equivalent circuit of the transducer, representing a general one-dimensional (1D) model, is first derived and presented in this paper. The general 1D model takes into account all existing transducer components, including both central bolts, in addition to the proposed 3D model. Additionally, when effects of the bolts are excluded, the resonance frequency equation was analytically derived based on the general 1D model. The composite transducer is designed and manufactured. For a large number of electrical connection combinations, transducer resonance frequencies are measured and compared with the results obtained from 3D and 1D models. The results indicate that the resonance frequencies obtained from 1D model are in line with the measured frequencies for the first thickness mode only. However, for all thickness and radial oscillation modes and their mutual coupling the analytically obtained frequencies from 3D model correspond well to the measured frequencies. In addition, the presented results in this paper contribute to a better understanding of the geometry and material properties of the composite piezoelectric transducer parts impact on transducer behavior.