This article describes the design of a multi agent software model to identify, synthesize and reuse knowledge all along engineering design projects. As a matter of fact, these projects require that engineers, with different specialities, collaborate to carry out the same goal. Inside professional processes, they use their know-how and knowledge in order to achieve the laid down goals. Our approach consists in using an organisational approach to identify the competences and knowledge of professional actors which allows the design and the description of agents' know-how. Furthermore, the paper describes the design of our agent model based on an organisational approach and the role of a domain ontology called OntoDesign to manage heterogeneous and distributed knowledge.