Abstract: Based on the micro-mechanical model , micro elastic-plastic and micro damage analyses are further carried out . The mat rix is assumed to be Von Mises elastic-perfect-plastic material. The average st ress over the entirelength of the mat rix cylinder is used to predict the yield of the mat rix material. The plastic zone is simplified to expand axi-symmet rically under plastic loading1 A unified damage criterion is proposed for both mat rix damage andparticle/ mat rix interface failure , considering the short length of the mat rix cylinder in the micro model for composites with high volume f ractions of particles1 The effect s of principal st rain and t ri-axial st ress state are also considered in the damage criterion. A decreased macro modulus is obtained by averaging spatial dist ributions of microyielding and damage. Uniaxial tensile and compressive behaviors of a particle reinforced metal mat rix composite aresimulated by using the proposed method1 The simulations are in good agreement with experimental data.