Abstract: An mesomechanical model that can simulate the fracture process of concrete is proposed and used to study the facture characteristics of concrete under uniaxial or biaxial loadings based on knowledge of heterogeneous structure of concrete at the mesoscopic level. The biaxial strength envelope of concrete is numerically presented and compared well with experimental results. This model is able to capture the complete fracture process of concrete materials that includes the initiation, propagation and coalescence of microcracks as well as cracking patterns associated with different loading stages and loading conditions, which shows good agreement with corresponding experimental results.