Abstract: As an effective method for efficient precision machining of hard and brittle materials, ultrasonic-assisted machining has been widely researched and applied over the past years. As a result, higher requirements are put forward for the performance of ultrasonic-assisted machining equipment. The ultrasonic transducer is one of the core components of an ultrasonic-assisted machining system, which determines its machining performance. The study on the design method of an ultrasonic transducer is necessary for the establishment of an ultrasonic-assisted machining system. The four-terminal network method based on mechanic-electric analogies is an effective design method, which regards the mechanical vibration system as an electrical four-terminal network. The wave velocity of the mechanical wave in the vibration system can be equivalent to the current in the equivalent circuit, and the force impedance at both ends of the vibration system can be equivalent to the electrical impedance at both ends of the equivalent circuit. The size of the ultrasonic transducer can be calculated according to the electromechanical similarity theory and vibration boundary conditions. However, the conventional four-terminal network design method of the piezoelectric ultrasonic transducer (PUT) neglects the electromechanical coupling process inside the stacked piezoelectric ceramics (SPCs). The PUT designed by this method has a big size error and low output amplitude. Aimed to obtain a higher ultrasonic amplitude of PUT, the equivalent six-terminal network of SPCs considering electromechanical coupling is introduced into the traditional design method, and two PUTs of different sizes are designed by the four-terminal network and the six-terminal network, named transducer A and transducer B, respectively. The natural frequency and output amplitudes of the two PUTs are analyzed and compared by the finite element method, and the experiments further verified the validity of the theory and the simulation analysis. When the excitation voltage is the same, results show that the output amplitude of transducer B (designed by the six-terminal network) is 1.5 times higher than that of transducer A. Finally, applying a six-terminal network to the PUT designing can improve the vibration performance of the PUT effectively.