Computer Aided Design (CAD) and Computer Aided Engineering (CAE) are two significantly different disciplines, and hence they require different shape models representations. As a result, models generated by CAD systems are often unsuitable for Finite Element Analysis (FEA) needs. In this paper, a new approach is proposed to reduce the gaps between CAD and CAE software's. It is based on new shape representation called mixed shape representation. The latter simultaneously supports the B-Rep (manifold and non-manifold) and polyhedral representation, and creates a robust link between the CAD model (B-Rep NURBS) and the polyhedral model. Both representations are maintained on the same topology support called the High Level Topology (HLT), which represents a common requirement for simulation model preparation. An innovative approach for the Finite element simulation model preparation based on the mixed representation is presented in this paper, thus a set of necessary tools is associated to the mixed shape representation. They help to reduce the time of model preparation process as much as possible and maintain the consistency between the CAD and simulation models.