This paper takes Chinese manufacturing listed companies as the research object, investigates the possibility of the promotion role of assurance service of external auditors instead of internal relational governance in the value creation effect of supplier relationship. It arrives at the conclusions that close relationship between firms and their key suppliers can significantly enhance corporate value, and simultaneously reduce firms' demand for high quality audit assurance services, but the reduction in the demand for high quality audit assurance services does not weaken the promotion role of supplier relationship in corporate value, showing that there is a substitution relationship between internal relationship governance and high quality audit assurance services. At the same time, with the improvement of external institutional environment, the substitution effect above-men-tioned weakens. This paper provides more direct evidence for the understanding of the joint effects of external audit assurance&relationship networks in transition economy&society mainly featured by relationship governance on corporate value creation, and further enriches&extends the literature of the effect of relationship-based exchanges on corporate value from the perspective of external audit assurance.