Using the quasi-natural experiment of the China's Golden Auditing Project, we select A-share state-owned listed companies from 2008 to 2020 as samples to empirically test the effect and mechanism of national audit informatization construction on audit fees of state-owned enterprises. It is found that the construction of national audit informatization has significantly reduced the audit fees of state-owned enterprises, this spillover effect can be achieved by reducing the auditor's effort and improving the quality of internal control of state-owned enterprises. The heterogeneity test shows that the effect of national audit informatization construction on reducing audit fees of state-owned enterprises is mainly reflected in the international “Big Four” audit enterprises, the enterprises that issued standard unqualified opinions and the enterprises that did not have financial restatements. The extended analysis finds that the application of digital technology, hardware investment and media attention significantly enhance the inhibitory effect of national audit informatization construction on audit fees of state owned enterprises. The research conclusions have implications for clarifying the internal mechanism of national audit affecting social audit under the digital situation, improving the efficiency of audit resources allocation, and forming a collaborative and efficient audit supervision system.