Abstract: The deformation, damage, and failure process in particle filled composite are studied by using a numerical code, MFPA2D, newly developed by CRISR at Northeastern University, Shenyang, P.R.China. Two kinds of particles, rigid and soft with high strength, are considered. The single particle is studied firstly, then multiparticles are modeled. The results from both the single particle model and the multiparticle model show that the failure mechanisms are strongly dependent on the particle stiffness. The simulations reproduce the crack initiation, propagation and coalescence in brittle and heterogeneous matrix. Interactions between the particles are also modeled. The numerical analysis elucidates the effect of the particle stiffness on the anticipated strength and toughness of the matrix.