Based on the sample of Shanghai and Shenzhen A share listed companies from 2015 to 2018, this paper studies whether the inquiry letter of financial reports can exert regulatory spillover effect in the audit connection from the perspective of readability of annual reports. The study found that the readability of the annual report of listed companies (issuers) improved after being questioned, and the readability of the annual report of companies (recipients) with an audit connection also significantly improved, that is, the inquiry letter had regulatory spillover effect. Especially when the investors of the issuers pay high attention, the media report much, or the market competition is fierce, the regulation of inquiry letter is more likely to produce a spillover effect, which can significantly improve the readability of the annual report of the recipients linked by audit. Further research shows that the heterogeneity of inquiry letter characteristics and audit connection characteristics has a different impact on the regulatory spillover effect of an inquiry letter.