Abstract: In China’s capital market, it has become a notable anomaly of firms making large-scale fixed asset purchases in the fourth quarter, with investment volumes far exceeding those of the preceding three quarters. Using the data from A-share listed companies between 2007 and 2022, this study examines the impact of corporate abnormal investment on audit opinions issued by auditors. The findings reveal that corporate abnormal investment will increase the probability of non-standard audit opinions being issued by auditors. The mechanism tests show that corporate abnormal investments can lead to earnings management behavior and widen book-tax differences, thus increasing the probability of non-standard audit opinions being issued by auditors. Further analysis indicates that compared to enterprises with high abnormal audit fees and high internal control quality, enterprises with low abnormal audit fees and low internal control quality are more likely to receive non-standard audit opinions from auditors. For this reason, auditors should carefully identify abnormal investments in enterprises, and the regulatory authorities should increase their supervision of abnormal investments in enterprises.

Key words: abnormal investment, audit opinion, earnings management, book-tax differences.