Abstract: Microcracks control the macroscopic mechanical properties and fracture behavior of rock, and their distribution is uncertain. Existing researches on rock crack growth focus on deterministic crack growth law, with the influence of random microcracks insufficiently accounted for. In this paper, based on the theory of Peridynamics (PD), random distribution function is introduced to preset the geometric and positional parameters of microcracks, and a large-scale Monte Carlo simulation is conducted on the tensile failure process of rock components with macro cracks and random microcracks. The failure probability factor of material point (PFP) is proposed to describe the failure probability of material points, and the influence law of random microcracks on tensile macroscopic crack propagation of rock is revealed. By analyzing two classical examples, the results are found to be consistent with FEM and XFEM. In addition, rock components containing macro cracks and micro cracks are introduced in this paper. According to the random distributions of the position, angle, and length of micro cracks, PFP cloud images under different conditions are drawn for the first time. The influence law of each parameter on crack development is obtained. In this paper, the failure probability factor of material point fracture is first developed to quantitatively describe the effect of microcracks on macroscopic cracks propagation, which provides a new idea and method for predicting the crack propagation of rock containing random microcracks.