Grinding force and stress in the ultrasonic assisted grinding (UAG) influence on the material removal behaviour. In this study, the simulation investigation of the material removal process, by ultrasonic assisted scratching (UAS) of silicon carbide using a single abrasive grain in UAG was conducted, to reveal the grinding force and stress variation behaviour. Conventional scratching (CS) without ultrasonic vibration was also carried out on the same condition for comparison. The results showed that: 1) the cutting forces in UAS undergo a periodic sinusoidal change, whereas those in CS are basically stabilised to a certain level after the tool cuts into the workpiece completely; 2) the stress distribution fields on the cross and top surfaces along the cutting direction become wider in UAS than in CS; 3) the kinetic energy of the grain consumed in UAS is bigger than that in CS, leading to the impact of the grain on the workpiece.