Abstract: With further development of economic globalization and market economy, enterprises form complicated relationships through equity, guarantees, mutual insurance, connected transaction, financial derivatives, supply chain and the multiple identities of management and so on. As a result, the associated credit risk has become hot and difficult problems in risk managements of modern enterprise. Under the framework of small world network, this paper proposes the concept of "small world networks based on the affiliated enterprises cluster network". we apply mean field theory and principle of epidemiology in order to construct associated credit risk contagion model between enterprises based on asset-related relationship under the imperfect immunization scenario, to reveal and simulate the relation among associated credit risk contagion probability with imperfect immunization and asset-related in enterprises cluster network. The study finds that the threshold value of the associated credit risk contagion is reduced under the condition of the immune failure and immune invalidity, thereby, increasing the likelihood of related credit risk contagion; and the assets correlation between enterprises will influence associated credit risk contagion and immune effect. The study of this paper is helpful for the prevention and control of the spread of the associated credit risk in the affiliated enterprises cluster, it has far-reaching academic value and practical significance.

Key words: affiliated enterprises community, small world network, associated credit risk, imperfect immunization, contagion