Short fiber reinforced Al-base composite can be manufactured various parts by plastic working. Elastic modulus has a large influence on the parts among the composite system. In the paper, model of finite-element analysis has been established. The influences of interface modulus on the law of stress-strain distribution, the strength and the modulus for the composite materials have been simulated by ANSYS in the condition of strong-bond, medium-bond and weak-bond interface. The results show that the stress-strain distribution is non-uniform, moreover the force on the fiber is greatly higher than that of the matrix within the composite materials; the strength of the composite materials is improved with the increasing of the interface modulus, but the increasing will be limited by the strength of fiber. Therefore the relation of ideal interface modulus with the fiber strength has been proposed. 70GPa of the interface modulus is thought to be better for M40 short fiber.