Abstract: A discrete element mesoscopic numerical model which considers the aggregate gradation of reinforced concrete (RC) beams is established by PFC2D. The research on the ultimate bearing capacity and crack propagation law of RC beams is carried out. The accuracy of the meso-parameters of concrete elements is verified by uniaxial compression simulation of concrete standard prisms. Meanwhile, a parallel-hardening contact model which is modified by the parallel bond model is established for steel rebar simulation, and the uniaxial tensile simulation of steel bar has verified the accuracy of the meso-parameters. A discrete element numerical model of unnotched RC beam is established and the numerical model of pre-notched RC beam is generated based on unnotched RC beam. According to the notch position and dip, test conditions are divided into 9 types. The crack propagation law and ultimate bearing capacity of each test condition are analyzed. The results show that the notch position has great influence on crack propagation process, and the crack initiation positions are generally located at the tip of notch. The notch dip only affects the initial stage of crack propagation, and the cracks may continue to grow along the vertical direction in the later stage. The ultimate bearing capacity of pre-notched beam is about 95%~98% of that of unnotched beam.