Important audit procedures for certified public accountants to obtain audit evidence. Confirmation letter is an audit term, which is a process for auditors to obtain and evaluate audit evidence by directly stating relevant information and existing conditions to a third party in order to obtain information that affects financial statements or related disclosures. It belongs to an important audit procedure for certified public accountants to obtain audit evidence. Most of them are used for auditing and capital verification, and the evidence obtained through correspondence is highly credible.