Abstract: The effect of interface properties on failure modes in particle filled composite is studied by using a numerical code, MFPA^2D , newly developed by CRISR at Northeastern University, Shenyang, P.R.China. Two kinds of interface, ideal and non ideal, are considered. The single particle is studied firstly, then multi particles are modeled. The results from both the single particle model and the multi particle model show that the failure mechanisms are strongly dependent on the interface properties. 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 interface properties on the anticipated failure modes. In the ideal interface condition, the failure mainly occurred in the location near to the interface. However, in the non ideal interface condition, the failure mainly occurred in the interface, which results in the interfacial debonding.