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. This later, supports simultaneously 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. A new software environment for CAD/CAE integration based on the mixed representation is presented in this paper, thus a set of necessary tools is associated to the mixed shape representation which contribute to reduce as much as possible the time of model preparation process.