The mechanical properties of injection moulded plastic parts depend on the morphology, the degree of crystallinity and the molecular orientation of the formed microstructure. In order to take the variation of the microstructure into account in a structural analysis, a novel multi-scale, integrated simulation approach is presented here. At first, a coupled mould filling and heat transfer analysis is achieved at the macroscale and its temperature field is transferred to the micromodel. Based on the concept of cellular automata, a 3-D microstructure evolution model is developed. It specifies the nucleation of the spherulite germs and describes their expansion rate. To evaluate the effective mechanical properties of the simulated microstructures, the homogenisation method is applied directly to the spherulites, assembled in few classes according to their crystallinity degree. These local properties are then introduced into a new multilinear material model for structural analysis of thermoplastics. Finally, the influence of the microstructure on macroscopic behaviour is outlined for a polypropylene tensile bar, extracted from an injection moulded plate.