Abstract: Concrete is considered to be one of two-phase composite materials composed of cement matrix and aggregates. At meso-scale level, the digital image processing method is used as a measurement tool to construct a digital representation for the distribution and the shape of aggregates in concrete; and at micro-scale level, statistical method is used to describe the inhomogeneity of component materials. A multi-scale coupled numerical model that can simulated damage evolution of concrete under loading is proposed by taking into account the material inhomogeneity at micro-scale and meso-scale level. The failure process of concrete is simulated by this model under uniaxial stress. The computing results show that this model can take into account the influence of the distribution of aggregates and respective heterogeneity of component materials on mechanical performance of concrete and is able to capture the complete failure process of concrete materials that includes the initiation, propagation and coalescence of microcracks as well as cracking pattern associated with different loading stages.