Flexural vibration mode piezoelectric ceramic transducers can be used in many application fields because of their ability to develop large displacement at low levels of electrical excitation, or conversely, to generate high output from sources of low mechanical impedance. Many flexural transducers are very thin, and their behavior can be analyzed and predicted accurately by the current theory based on thin-plate assumptions. However, for those flexural transducers with moderate thickness, the thin-plate assumptions are no longer valid. To analyze and predict the behaviors of the flexural transducers with moderate thickness, we must establish a new theory. In this paper, by introducing Mindlin's assumptions and theory, the displacement function and equivalent circuit for circular flexural composite transducers with moderate thickness are derived. Through the displacement function and the equivalent circuit, the vibration characteristics and the electrical impedance of circular flexural composite transducers with moderate thickness can be predicted directly.