Abstract: A 2D orthogonal composite sandwich piezoelectric ultrasonic transducer excited by four piezoelectric stacks is proposed by using a central coupling metal block, four piezoelectric stacks and four front conical metal mass. Based on the principle of 2D coupled vibration and the electro-mechanical analogy principle, the equivalent circuit model of the transducer is established and its resonance frequency equation is derived. The finite element software is used to simulate and analyze the frequency response characteristics and vibration characteristics of the transducer, and compared with the vibration characteristics of a single directional vibrator of the transducer. The transducer of anti-phase mode and the transducer of in-phase mode were processed. Their frequency response and 2D four direction longitudinal vibration output characteristics were measured by the impedance analyzer and the laser vibrometer, and the transducer of in-phase was tested by the high-power 2D four direction ultrasonic emulsification experiment. The theoretical, the simulated and the experimental results demonstrate that the transducer has two longitudinal orthogonal vibration of anti-phase and in-phase modes, and 2D four-directional longitudinal vibration output is achieved in both resonance modes. In addition, the longitudinal vibration of the two orthogonal vibrators of the transducer has the effect of mutual coupling and strengthening. The resonance frequency and the effective electro-mechanical coupling factor of the transducer calculated by the equivalent circuit method and the finite element method are basically consistent with the results of the experiment. By comparing with the effective electro-mechanical coupling factor of the 2D orthogonal composite sandwich piezoelectric ultrasonic transducer excited by single piezoelectric stack, it is found that the transducer excited by four piezoelectric stacks has a greater effective electro-mechanical coupling factor.