This paper focused on improving machining precision and reducing the machining errors caused by tool wearing in a Rotary Ultrasonic Grinding Machining(RUGM). The relation model between the ultrasonic vibration tool life and the grit sizes, grit concentration and the inner circle radius of a tool was established, and the parameters affecting ultrasonic vibration tool life were optimized. First, the second order model of ultrasonic vibration tool life was established for a bronze-bonded ultrasonic vibrating tool with Response Surface Methodology (RSM), and the model was fitted based on Box - Behnken experiments. Then the ultrasonic vibration tool life model was checked by effectiveness and significance tests. Finally, the cross-fertilization between the various influence factors and the tool life was analyzed through fitting the response surface and the contour between ultrasonic vibration tool life and factors, and the ultrasonic vibration tool parameters were optimized. The results indicate that the wear capacity of ultrasonic vibration tool is only 0.006 9 mm, after removing 9 600 mm3 for Si3N4 ceramics materials with density of 85%, when the grit size is D98.85, grit concentration is 77.36, and the inner circle radius of the tool is 5.34 mm. It satisfies the finish machining requirements for RUGM.