Abstract: Based on the single fiber axisymmetrical and three dimensional models of an aligned short fiber reinforced metal matrix composite, the effect of varied fiber aspect ratio on the mechanical behavior of this composite is analyzed by the elasto-plastic finite element method. The studies are focused on the stress transfer, elastic modulus and stress-strain curve of the composite. It is shown that, in this kind of composite, the fiber aspect ratio has an optimum range. The composite with a good performance cannot be obtained with a too small fiber aspect ratio. However, when a critical value is reached, the performance of the composite does not increase with the fiber aspect ratio any more.