The aim of this study is to determine the nonlinear relationships between company characteristics and the level of internal audit performance based on information asymmetry and intra-company monitoring (case study: companies in the Assaluyeh Special Zone). The research method was descriptive-survey and applied, and the research data were collected cross-sectionally in the first half of 1403 through a questionnaire that was distributed among the sample members and collected over a specific period of time. The validity was assessed in the form of face validity and data reliability using the Cronbach's alpha test and its regression analysis. In this regard, the statistical population is the companies in the Assaluyeh Special Zone, and the statistical sample includes 169 managers, employees, experts, and financial engineers, and auditors active in the company, who were selected using the Morgan table method. The results of the study indicate that there are significant nonlinear relationships between company characteristics and the level of internal audit performance based on information asymmetry and intra-company monitoring (case study: companies in the Assaluyeh Special Zone). Therefore, company characteristics such as company size, number of employees, number of subsidiaries, and intensity of use of internal audit by different shareholders can lead to changes in the level of internal audit performance based on information asymmetry and intra-company monitoring.