3D computer aided design (CAD) system based on feature-based solid modeling technique has been widely used for product design recently. At the same time, CAE also plays a more and more important role in product design and finite element method is one of the most popular CAE methods. The models built by CAD systems usually need simplification before finite element analysis according to precision need. How to analysis the degree of simplification is an essential problem in automatic transformation from CAD model to CAE model. Models of different degree of simplification are called Multi-state Model. Considering the need of economizing hardware resource and ensure the appointed correction precision at the same time, this paper proposes a measurement method of the error of different simplification models according to FEM error analysis theory and then validates that by numerical results. Based on the measurement method, the concept of Level of Error is proposed, which provides a new way of getting Multi-state Model in FEM field.