On the basis of establishing a mechanical model of brittle materials(rock)cutting,the finite element method was used to analyze a mechanical behaviour shown inthe cutting process,and the initiation and propogation of crack at initial stage,after pene-tratim of cutting blade,were simulated. The results have shown that it is feasible for theless interior defect rock to judge an initiation of crack by the stress criteria,The cracktypes are related to material brittleness index. The cutting resistance is increased with theincrease of cutting depth and shows a non- linear increase. The initial path of crack pro-pogation is related with a rake angle of the cutting blade.