The mechanical behavior of binary polymer blends polystyrene/polypropylene were studied by a continuous mesoscopic simulation method. The dynamic density functional theory approach embodied in MesoDyn method was adopted to obtain the meso-structures of polymer blends. The output of MesoDyn serves as the input of a micromechanical lattice spring model (LSM), which consists of a three-dimensional network of springs. Mechanical properties, such as young's modulus and stress distribution can be obtained through applying strain in LSM. Subsequently, a stress-related probabilistic method was applied in LSM to study the fracturing process of materials. The fracture positions were shown in detail which have close relationship with the meso-structures. Due to the significance of interface which has a notable influence on the global mechanical properties of immiscible blends, we proposed a new method to define the stiffness in the interfacial area to study the global stiffness (young's modulus) of materials. The results show a good agreement with the existing experiments. Besides, we varied the minimum fracture stress (related to toughness) of the interface to investigate the strength of polymer blends. A graphic representation was shown in this work, it indicates that the system with continuous interface perpendicular to the applied strain are more likely to exhibit catastrophic failure. The methods developed in this work provide important tools to predict the mechanical properties of real polymer blends. (C) 2011 Elsevier Ltd. All rights reserved.