Considering the increasing importance of internal audit in creating added value for the organization and considering the improvement of its process using knowledge management, the purpose of this study was to develop a model for internal audit based on knowledge management using action research. For this purpose, the internal audit unit of Golrang Industrial Group has been used as a case study. At the beginning, a number of weaknesses were identified by interviewing the managers and staff of the unit. In the next stage, the weaknesses were refined and classified so that the weaknesses were divided into two categories: weaknesses related to underlying issues and weaknesses related to the executive stages. underlying weaknesses include 1-human resource management weaknesses, 2-training-related weaknesses and 3-weaknesses of macro issues. Besides, the executive stages are divided into four categories: 1- Cognitive and evaluation stage weaknesses, 2- Planning stage weaknesses, 3- proceeding stage weaknesses, and 4- Reporting and follow-up stage weaknesses. The focus of this research has been on the weaknesses of the executive stages. Then, knowledge management tools were identified to eliminate weaknesses and improve the points that can be enhanced in the implementation stages of internal audit and then they were implemented during a reciprocal process and after adjustment and correction and reaching an optimal state. In the last step, after evaluating the effectiveness of the tools used, the conceptual and final model of the research is obtained.