Cooperative design is a complex group activity that involves participants with heterogeneous skill. In this paper, a cooperative design approach in a multi-agent design system is introduced and a form of Bulletin Board that supports dynamic task assignation and a kind of conciliatory approach when conflict occurs in design are presented. According to autonomous and cooperative features, the form of Bulletin Board combines the advantage of black board and contract-net and introduces a style of distributed and centralized combination, weakens some failings of black board and contract-net during dynamic assignation in distributed environment. Then, it puts forward a conflict pre-checking and conflict processing approach. This approach aims at finding and solving conflict during the early design phase and decreasing resource waste.