Abstract: In this paper，a numerical code of RFPA was applied to simulate the rock fracture mechanism under disc cutters of TBM．The fracture processes of rock specimens with confining pressure subjected to a single cutter，double cutters and three cutters were investigated respectively，and the cutter spacing was optimized under the action of multi-cutters．The results show that the whole fracture process under the action of single cutter has four stages: powder formation，crack nucleation，side crack initiation and propagation，and chip formation，and the rock fracture is dominated by tensile stress，accompanied by shear stress and compressive stress，etc．Under the confining pressure，the cracks parallel to confining pressure are easier to initiation and propagation，and more beneficial to the coalescence of side crack．Moreover，obvious synergistic effect is found between the neighboring cutters，and with the increase of cutter spacing，the specific energy consumed to rock fracturing increases in the beginning stages，and will decrease，when the spacing is beyond a critical value．The simulation results agree well with experimental ones，and will be beneficial to TBM design and disc cutter arrangement.

Key words: rock breaking under disc cutter, crack propagation, cutter spacing optimization rock breaking under disc cutter, crack propagation, cutter spacing optimization rock breaking under disc cutter, crack propagation, cutter spacing optimization rock breaking under disc cutter, crack propagation, cutter spacing optimization rock breaking under disc cutter, crack propagation, cutter spacing optimization