The influence of hydrostatic pressure on rock-cutting based on Voronoi grain bonded-cluster model is investigated in this paper. Unconfined compressive strength and Brazilian tests are performed to calibrate the relations between micro-properties and mechanical properties of the rock sample. The influences of hydrostatic pressure, cutting velocity and cutting depth on rock-cutting are researched by particle flow code in 2 dimensions. With no hydrostatic pressure, the fractures in the upper area developed rather quickly into the rock along the horizontal direction when the cutter penetrates over 4 mm. The horizontal crack could eventually arrive at the free surface causing a large volume of fragment chips. Hydrostatic pressure could significantly influence the fracture evolution, inhibiting the formation of the long horizontal fracture. The influence of hydrostatic pressure on rock cutting becomes more and more obvious when the hydrostatic pressure is over 5 MPa. High hydrostatic pressure could inhibit the development of the fractures, increasing the energy requirements of drilling and effectively strengthening the rock. The influence of velocity on rock cutting is not obvious when the cutter penetration is less than 1 mm. However, the fracture volume presents a decreasing trend as the cutting velocity is increasing. There is an optimal cutting velocity for rock cutting, the corresponding optimal cutting velocity is 300 mm/s with high rock fragmentation efficiency. As the cutting depth increases, more and more micro-cracks are initiated around the cutter and the volume of the chipped fragmentation is increasing correspondingly. According to the simulation, it is believed that Voronoi grain-based model will contribute to a better understanding for the rock-tool interaction.