Pre-slotting rock is an effective method for improving the rock cutting performance of mechanical cutting tools. A method of rock cutting using a disc tool assisted by vertical pre-slotting on free-face has been proposed, and in this paper, the effect of the number and configuration of pre-slots on the improvement of rock cutting performance is evaluated. The progress of crack propagation is analyzed, and the underlying mechanism is revealed under different pre-slots conditions with the help of DEM. Considering the effect of confining stress under actual conditions, the rock cutting performance using a disc tool and the enhancing effect of pre-slots are investigated. The results show that the mean cutting force decreases with increasing pre-slots spacing when the pre-slots spacing is less than the diameter of the disc tool, and the reducing ratio of the cutting force is more than 40 % with 80 mm spacing under the two pre-slot conditions. A large number of pre-slots destroy the integrity of the rock, and the cutting force under the condition of four or five pre-slots decreases by more than 50 %. The confining pressure suppresses the propagation of tensile cracks, the cutting force increases linearly, and the ratio of tensile to shear cracks decreases with increasing confining pressure. The confining pressure weakens the improvement effect of pre-slots assisting rock cutting using a disc tool to a certain extent, while under the condition of five pre-slots, the improvement is further developed, in which the cutting force decreases by 60 % at a 20 MPa confining pressure.