As a kind of informal system, the social capital of enterprises has a alternative to the formal system, prompting the formation of commonly accepted norms and mutual expectations among enterprises, thus reducing the opportunistic behavior and reducing the costs in economic transactions Certainty, which can effectively reduce transaction costs. The enterprises with social capital and their external stakeholders establish deep trust in the long-term repeated game process, establish good market reputation and social reputation, greatly reduce the transaction cost of negotiation, signing, consultation, execution and supervision, thus bringing excessive profits to the actors in the relationship network structure.In the path of the impact of corporate social capital on transaction cost savings, trust mechanism, information transmission mechanism and socialist preventive mechanism play an important intermediary role.