Model transformations are touted to play a key role in model-driven software development. The mapping relations between different models are the foundation and basis for the transformation. A classification for different level mappings was proposed and defined formally by abstractly analyzing the characteristics of syntax and semantic features of modeling languages. On this basis, a further study about the simulation-based mapping approach was conducted to explore the definition process for mapping relations and the cardinal principles should be followed. The UML-based class model used as a source and the C programming language used as the target are shown in the case study to help interpreting the ideas. It may not only be a theoretical guidance for model transformation, but also can be a measurement for validating the mapping rules between models at different abstract levels.