The confidentiality of relationship transactions determines the opacity of public information disclosure. Using the quasi natural experiment of the Shanghai Stock Exchange mandatory disclosure requirements for audit committee duty performance information in 2013, and applying the difference in differences model, this paper examines whether and how the increased transparency of audit committee affects the supplier/customer relationship transactions of listed companies. The results show that the improvement of audit committee transparency has a positive effect on supplier/customer relationship transaction in the short term, which may be related to the credible commitment delivered by the policy, and information users have more trust in the information disclosure. In a long run, however, this effect has weakened. Further research shows that only companies in areas with a better legal environment or/and higher social trust, the increasing of their audit committee transparency can facilitate the supplier/customer relationship transaction, which verifies the role of trust mechanism. In addition, the increased transparency of audit committee eases corporate financing constraints by facilitating the supplier/customer relationship transactions. The above results enrich the study of the influence factors of relationship transactions at the corporate information environment level, and provide empirical evidence to evaluate the implementation effects of the audit committee information disclosure reforms.