Abstract: A Y-type sandwich piezoelectric ultrasonic transformer is proposed. Based on the coupled vibration theory and the principle of electromechanical analogy, the electromechanical equivalent circuit model of the transformer is established, and its resonance/anti-resonance frequency equation, voltage gain and power gain expressions are derived. The power transfer characteristics and electromechanical conversion characteristics of the transformer are studied by equivalent circuit method, finite element simulation and experiment. The results show that in the resonance mode, the Y-type sandwich piezoelectric ultrasonic transformer has the smallest input reactance and the largest voltage gain and power gain, which is expected to be used in the electronics field as a dual-channel piezoelectric transformer.