Ultrasonic vibration-assisted technology is widely concerned for its advantages of weakening rock strength， reducing cutting force and accelerating drilling speed. The combination of ultrasonic vibration technology and the disc cutter can effectively improve the construction efficiency in hard rock in tunneling. The process of rock breaking by the disc cutter assisted by ultrasonic vibration is simulated with the particle flow discrete element software. The results show that ultrasonic vibration can produce a periodic stress wave and propagate into rock with strong tensile stress appearing in the near surface area of rock， which is conducive to the tensile failure of shallow rock. Ultrasonic vibration can enhance the crack formation scale inside rock， accelerate the crack formation speed， and advance the crack initiation time， amplifying the rock breaking performance of the disc cutter. With ultrasonic vibration， cracks grow more stable in rock， which reduces the phenomenon of leap-forward crushing， and can avoid the abnormal wear and damage of the disc cutter caused by the impact load caused by the violent vibration， which can help extend the life of the disc cutter.