Abstract： Supply chain provides correlative organizations from industrial upstream and downstream with a platform of interactive relationship. Based on the perspective of ecological theory, five modes for the interactive relationship of organizations in the supply chain are concluded; they are malignant competition, reciprocal cooperation, dependent development, aggressive relationship, and damaging growth. And different relationship models are built up. By qualitative analysis of differential equation and numerical simulation for these models, it is pointed out that different organizations gain different benefits and follow diverse strategies in the interactive relationship, and furthermore the evolution mechanism of organization structure in a supply chain is revealed.