The effects of multiple ultrasonic frequencies on grinding surface quality of Al2O3-ZrO2 nano-composite ceramics are researched to provide optimization laws for ultrasonic grinding parameters. Some SEM photographs of ultrasonic grinding surface with different frequencies are provided to research the surface quality. The enhanced surface quality of ceramics with ultrasonic grinding is explained as the transition of single abrasive particle removal mode from brittle to ductile, which is resulted from the reduction of equivalent rigidity on surface under ultrasonic vibration. And this phenomenon becomes more evident as frequency increases. Through the XRD experiment, the phase transition from tetragonal phase t-ZrO2 to monoclinic phase m-ZrO2 becomes increasingly obvious by the action of ultrasonic vibration. The compressive stress generated during this phase transition can suppress the initiation and expansion of microcracks on the processing surface. The research shows that, the grinding surface quality with ultrasonic vibration is superior to that without ultrasonic vibration, and increasing ultrasonic frequency can contribute to the improvement of the surface quality.