With the deepening of drilling depth， breaking hard rock formations became more difficult， and increasing rotational speed has become one of the feasible methods to break hard rock formation rapidly and effectively. The impregnated diamond bit has a good application effect in the hard rock formation， the interaction mechanism between the impregnated bit and rock is relatively perfect at conventional speed， and there is also a corresponding application and research basis at high speed and ultra-high speed. However， the rock fragmentation mechanism at high speed to ultra-high speed is not completely clear. Based on the interface laws for impregnated diamond and rock， a two-dimensional model of single diamond cutting rock is established by using ABAQUS software， and an approximate analysis method is proposed to define and calculate the nominal “tool tip” position， and further derive the force expression of single diamond， in order to explore the rock cutting force and changes of hard rock breaking from conventional speed to high speed and ultra-high speed by single diamond. The result shows that the cutting action of single diamond on rock is mainly concentrated in the middle and upper part of the interface between the cutting tool and the rock. The cutting force of a single diamond at high speed is lower than that under conventional cutting speed， and the main action part is affected by the change of cutting speed. There are plastic fracture and brittle fracture in the interaction between diamond particles and rock， and the two failure modes occur alternately. The proportion of brittle fracture at high speed increases compared with conventional speed， and the fluctuation range of cutting force at high speed is smaller， and the he energy required for rock breaking is much less. An approximate analysis method of rock-breaking response of the impregnated diamond bit is proposed， which equals the diamond particles as a cutting tool with “tip” and “front and rear” through analysis， the force expression of single diamond which is related to factors such as cutting speed and cutting depth is derived， and force is. The research results can provide a basis and reference for further research and application of breaking hard rock formations with increased rotational speed.