Abstract: The elastic modulus of polypropylene/polystyrene (PP/PS) blend was predicted by means of meso-mechanics of composite materials. Based upon the systematical studies of the effects of composition and mixing time on the elastic modulus and morphology of immiscible blends PP/PS, the relation of microscopic morphology and macroscopic mechanical property was discussed. Tensile tests showed that the meso-mechanical models were valid for the prediction of elastic modulus, and Mori-Tanaka model would be a more effective method for designing materials in comparison with Halpin-Tsai model and modified mixture model because there is no restriction on the experimental parameters.