The purpose of this study is to investigate the effect of conflict management quality on the performance of the North Tehran Freeway Project with the mediating role of flexibility. The study population is managers and experts of the North Tehran Freeway Project. Given that the size of the statistical population in this study is 280 people, and according to the Cochran formula, the required sample size is 162 people. In this study, a standard questionnaire was used to collect data. The questionnaires were distributed and collected using a rando maccess method. To analyze the data, structural equation testing with partial least squares was used using SMART-PLS software along with descriptive statistics. The test results at a 95% confidence level showed that the quality of conflict management, with the mediating role of flexibility, has a positive effect on project performance (p<0.05). The quality of conflict management has a positive effect on project performance. The quality of conflict management has a positive impact on flexibility. Flexibility has a positive impact on project performance. Therefore, project managers with the appropriate conflict management style and flexibility can partially reduce the possible consequences of destructive conflict, including increased costs, severe reduction in communication between individuals and groups, resistance to change, increased tension and stress, failure to deliver projects on time, poor performance, and unhealthy business relationships.