An aggregate generation and packing algorithm based on Monte-Carlo method is developed to express the aggregate random distribution in cement concrete. A mesoscale model is proposed on the basis of the algorithm. In this model, the concrete consists of three parts, namely coarse aggregate, cement matrix and the interfacial transition zone (ITZ) between them. To verify the proposed model, a three-point bending beam test was performed and a series of two-dimensional mesoscale concrete models were generated for crack behavior investigation. The results indicate that the numerical model proposed in this study is helpful in modeling crack behavior of concrete, and that treating concrete as heterogeneous material is very important in fracture modeling. An aggregate generation and packing algorithm based on Monte-Carlo method is developed to express the aggregate random distribution in cement concrete. A mesoscale model is proposed on the basis of the algorithm. In this model, the concrete consists of three parts, is a coarse aggregate To verify the proposed model, a three-point bending beam test was performed and a series of two-dimensional mesoscale concrete models were generated for crack behavior investigation. The results indicate that the numerical model proposed in this study is helpful in modeling crack behavior of concrete, and that treating concrete as heterogeneous material is very important in fracture modeling.