In elastic deformation range, this paper reports a finite element study of effect of length and diameter of the fiber on intrfacial stress of AZ91D metal matrix composites reinorced by short fiber. The nuit cell model is developde in ansys. It was found no infuence the fiber length has on the interfacial regions. There is considerable increase in intefacial von-Mises stress near the fiber end with increase in fiber diameter, and the region of stress transfer become wider. So, the risk of crack and debonding increase.