Abstract: The supplier, contractor and client constitute a supply chain in engineering procurement.Through long-term construction and purchase, the client and the contractor have the motivation of cooperanon.Based on evolutionary game theory, the paper studies the evolutionary direction of co-opetition between client and contractor, and analyzes the influencing factors.The result shows that the probability of cooperation of both sides has a positive correlation with excess return and a negative correlation with cost of cooperation and betrayal income.Reasonable partition coefficient to distribute the excess return is a necessary condition for both sides' sustained cooperation.In the case of an alliance contract, betrayal will be punished, and cooperation of both sides will be the evolutionary direction.

Key words: engineering procurement, supply chain, co-opetition, evolutionary game