Abstract: Based on homogenization method, a representative volume element (RVE) of discontinuous long glass fiber reinforced composites was constructed according to the microstructure of the composites. The equivalent elastic mechanical properties of the composites were obtained based on a numerical simulation on the RVE, and were then compared with the experimental data of the tensile properties of injected spline. Numerical results show that it is more reasonable based on the new finite element model built by adding polypropylene(PP) at both ends of glass fiber than on the traditional one which applied on continuous fiber reinforced composites. Glass fiber reinforced polypropylene is transversely isotropic when glass fibers are unidirectional. In addition, the equivalent elastic modulus in the tensile direction first decreases slightly, then drops rapidly, and then turns stable with the increase of the angle between fiber orientation and tensile direction. In conclusion, homogenization theory is very useful for the prediction of the equivalent elastic mechanical properties of discontinuous glass fiber reinforced moldings in engineering, and is significant to provide the scientific evidence for the analysis of structure service performance of the moldings.