Being a key step in grinding process, dressing of grinding wheel influences the whole grinding results, especially grinding quality. Because of its good dressing effect, a new dressing method assisted by ultrasonic vibration attracted researchers’ attention. In this paper, on the basis of the researches on dressing with single-point diamond dresser, physical model of ultrasonic dressing of grinding wheel were established. According to the physical model and the SEM photos of grinding wheel’s surface topography, the mechanism of ultrasonic dressing was brought to light. Through contrast experiments, based on roughness and micro-feature of the ground surface, the influence of ultrasonic dressing on grinding quality was researched.