The feasibility of ultrasonic vibration-assisted grinding in dental restoration has been preliminarily proved. Improving the machining quality of zirconia ceramics by controlling cutting force is the focus of the researchers. However, the existing feed direction cutting force model for ultrasonic vibration-assisted grinding does not take the ultrasonic vibration amplitude and frequency into account. This paper presents a mathematical model for feed direction cutting force in ultrasonic vibration-assisted grinding of zirconia under the consideration of amplitude and frequency, and assuming that brittle fracture is the primary mechanism of material removal in ultrasonic vibration-assisted grinding of zirconia. The effects of amplitude and frequency on the motion, effective cutting distance, and theoretical removal of an abrasive particle have been analyzed. Besides, the number of active abrasive particles is calculated with analyzing the influences of lateral cracks and ultrasonic vibration. The variation laws of cutting force and penetration depth of an abrasive particle during ultrasonic vibration-assisted grinding have also been analyzed. Therefore, the relationship between feed direction cutting force and input variables is predicted through the developed model. Finally, pilot experiments are conducted for the mathematical model verification. Experimental results show that the trends of input variables for feed direction cutting force agree well with the trends of the developed cutting force model. Hence, the mathematical model can be applied to evaluate the feed direction cutting force in ultrasonic vibration-assisted grinding of zirconia ceramics.