To assist a medium-sized enterprise manager to conducting a simulation project, a computer-assisted performance analysis and optimization (CPAO) tool has been developed and described in this paper. The contribution of this work is moving towards the rigorous proposed methodology, and not to case study results. The methodology of design and development of CPAO application is presented through a specific case of the production lines and the buffer stock design problem. A perspective of this work is to make extensions to the functional production system and to the cellular manufacturing systems