Abstract: Rock failure results from the process of internal crack initiation, propagation and coalescence intrinsically. A 3D numerical model based on the microscopic damage mechanics is employed to simulate the failure process of numerical rock specimens containing a pre-existing surface flaw subjected to uniaxial compression. The initiation, propagation and coalescence of wing cracks, shell cracks, anti-wing cracks and the secondary crack of shell cracks are reproduced in three-dimensional manner. Numerical results are obtained as follows: (1) anti-wing cracks are induced by the tensile stress after the stress release resulting from the propagation of wing cracks; (2) the shell cracks are predominated by III-type loading, and the wing cracks stop when they propagate ahead for a certain distance; (3) the secondary cracks of the shell cracks lead to the collapse of the whole specimen; (4) III-type fracture could not be obtained by III-type loading in rocks, and the shell cracks are induced by tensile stress in III-type loading; (5) due to the heterogeneities in rocks, it is difficult to find curved wing cracks and anti-wing cracks. The numerical results will be a good supplement of experimental investigation of surface flaw. The numerical code is proved to be a satisfactory tool to investigate the rock fracture in three-dimensional manner.