[Purposes] For the ultrasonic defrosting mechanism is unknown in finned-tube evaporators. [Methods]The frosting process and frosting rules on the cold surface is obtained through microscopic visualization method. The theoretical model of ultrasonic defrosting is established on the basis above, and the resonance band of frost crystals and shear stress value excited by ultrasonic vibration is calculated by using the finite element software COMSOL. The maximum adhesion stress of frost crystals is compared calculated results, and the feasibility of ultrasonic high-frequency vibration defrosting technology is theoretically illustrated. Simultaneously, an ultrasonic defrosting experimental bench is constructed on the evaporator of the air-cooled refrigerator, the vibration values of the evaporator under ultrasonic high-frequency vibration are obtained by laser vibrometer, and the actual defrosting effect is compared with the numerical simulation results. Finally, the energy consumption of ultrasonic defrosting is analysed. [Findings] The interfacial stress excited by ultrasonic high-frequency vibration is obviously greater than the adhesion stress between the frost crystal and the cold surface of 0.4 MPa, which significantly reduces the mechanical properties of the frost crystal and makes the frost crystal loose and fall off. The optimal ultrasonic loading mode on the heat exchanger is intermittent loading, and the intermittent time is affected by the ambient temperature and humidity, and the higher the ambient humidity is, the shorter is the intermittent time, and vice versa, the longer is the intermittent time. [Conculusions]The energy consumption of ultrasonic defrosting is about 1/4 of that of traditional thermal defrosting, which has the feasibility of engineering application.