The structural evolution and mechanical properties of hard soft block copolymers and their nanocomposites were investigated by a hybrid simulation technique. The dynamic density functional theory approach embodied in MesoDyn method is adopted to obtain the meso structures. Then the output from our morphological studies serves as the input of the lattice spring model (LSM), which is used to simulate the stiffness and critical fracture strain. The results reveal that the stress transfer between the polymer matrix and nanoparticles in different composites is critical to the stiffness enhancement. Adding nanoparticles in hard phase can increase the elastic modulus and maintain its high extensibility in dispersed structures. Overall, the methods developed in this work yield guidelines for formulating elastomeric nanocomposites with the desired macroscopic mechanical behavior.