Abstract: In the supply chain system consisting of an online agricultural product platform and an offline physical store of agricultural products, the benefit coordination of the O2O supply chain under the spillover effect of offline to online promotion is considered. Through Stackelberg game and system cooperation, the optimal decision-making under the decentralized and centralized mode is compared, and it is found that cooperation can make the distribution of supply chain benefits more reasonable. Subsequently, a joint contract of "cost sharing and order risk sharing" is established. The results show that the promotion spillover effect can expand the demand and promote the increase of the interests of both parties without affecting the offline interests; and that the joint contract can effectively coordinate the supply chain, increase the order quantity and promotion level, and realize the maximum benefit and win-win situation for all parties.

Key words: promotion spillover effect, O2O agricultural supply chain, joint contract of cost sharing and order risk sharing