The results of research in the field of artificial intelligence and intelligent computer system initiated the application of expert systems in CAD area of research. In the project, a conceptual development of system that helps engineer, acting as the environment within which the designer design, by using the available expert tools is presented. By analysing the characteristics of artificial intelligence methods and the possibilities of application of expert systems shows that, with our theoretical knowledge, and existing abilities to visualise and process engineering knowledge, there is no possibility of a usable expert system for design purpose. Based on the developed formal models of the design process in the project is proposed a development of a system that represents the environment that enables flexible exploitation of available expert systems and tools in a systematic way. The design process represented as a tree is a design plan. Nodes of the tree represent plan operators. Attributes of nodes are defined as the action, action requirements, the effects of the action, restrictions and relations decision. During the exploitation of the design, plan engineer can activate nodes of the plan at its own discretion, and thereby recorded plan can be exploited as the network. In the project, the structure of a system based on the design plan and syntax of plan notation, as well as the basic algorithms of critical subsystems: subsystems for the plan management and subsystems for explaining the situation during the plan execution.
