Abstract: Mechanical properties and the damage evolutions of short fiber reinforced metal matrix composites (MMC) were studied by a meso mechanics model numerically. A phenomenological cohesive interface was formulated to simulate the fiber/matrix interface damage while the Gurson-Tvergaard model was adopted to describe the matrix damage. Attention was focused on the effects of the meso parameters on the damage, strength and toughness of the MMC. The meso parameters considered here include interface strength and fiber's aspectratio. All the computations were made based on the cell model. The investigation revealed that, if the interface is weak, the interface debonding is the main reason causing the MMC's loading capacity decreasing; when the interface strength is strong enough, the fiber tends to break and the ultimate strength of MMC is dominated by the fiber's strength. The dependence of the distribution of the matrix damage on the interface strength was also depicted in this study.