A formalization of the concept of a complex system simulation model is proposed, as a family of models-components with the standard organization of simulation calculations. This family is closed under the integration of models-components into the model-complex, so it is possible to synthesize fractal complexity models, without changing the computation organization. A new approach to the description, design and implementation of simulation models of complex systems arises – the model synthesis and model-oriented programming, allowing to exclude imperative programming, and to get the high degree of parallelism in the executable code.