The purpose of the research is to "provide a structural model of factors affecting the quality of internal audit in the framework of the corporate governance system." The research method was mixed (qualitative and quantitative). In the qualitative section, primary data were collected with the help of interviews through ۱۸ people using the snowball method. According to the methodological process, during the three stages of open coding, central coding and selective coding, firstly, the codes related to the topic were identified from the large number of primary data types; Then, by means of continuous comparison, a concept was extracted from several codes, and in the same way other codes were also converted into concepts until finally ۱۱۸ concepts were obtained. In the next step, some concepts were put in the form of a category so that ۱۹ categories were obtained for this research. In the quantitative part, the designed questionnaire was made available to the internal auditors of capital market companies in the number of ۳۸۵ people with a non-random sampling method. The analysis of the data obtained from the questionnaire showed that ۵ categories appeared as the central category, which include: risk assessment, information and communication, control activities, internal control environment, supervision and monitoring. Other categories were placed in the five categories of causal conditions (۳ categories), background or context (۲ categories), intervening conditions (۳ categories), strategies (۳ categories), consequences (۳ categories) to be presented in the visual model.