The process of parameter choosing in vehicle overall design is a process of collaboration design, and is also a process of group decision optimization. The degree of cooperation and level of experts become the crucial standards in Computer Supported Collaborative Design because many decision-makers participating in the design process have different expertise and goals. This paper describes vehicle overall design parameter selection with a Multi-Objective Decision-Making optimization model, presents the concepts of non-cooperation degree and non-specialty degree, and uses entropy to describe the model. Furthermore, Particle Swarm Optimization (PSO) algorithm is employed to resolve the model and to get optimal parameter. In addition, we propose an effective expert system based on the model and actual design process. Finally, the effect of the non-cooperation degree and non-specialty degree on the result is discussed and the sensitivity of the proposed system analyzed in this paper.