Extracting structural information from mesh models is crucial for Simulation Driven Design (SDD) in industrial applications. Focusing on thin-plate CAD mesh models (the most commonly used parts in electronic products such as PCs, mobile phones and so on), we present an algorithm based on primitive fitting for segmenting thin-plate CAD mesh models into parts of three different types, two of which are extruding surfaces and the other is a lateral surface. This method can be used for solid model reconstruction in the SDD process. Our approach involves two steps. First, a completely automatic method for accurate primitive fitting on CAD meshes is proposed based on the hierarchical primitive fitting framework. In the second step, a novel procedure is proposed for splitting thin-plate CAD mesh models by detecting parallel extruding surfaces and lateral surfaces. The method presented here has been proved to work smoothly in applications of real product design.