The purpose of this study is to provide an optimal model of the impact of contractors' claims in three-factor construction projects with a system dynamics approach. Therefore, the purpose of the current research is fundamental at the national level, and because of this, the current situation is examined and analyzed. The current research is considered a type of system dynamics studies, in general, a mixed (quantitative-qualitative) method is used in system dynamics studies, in this research two statistical populations have been determined: theoretical experts: including university professors Azad Tehran South, whose expertise is in the field of designing and operating dynamic systems. Experienced experts: including experienced managers who work as managers of three-factor construction projects. And the theoretical method is used for the sample. Library and internet resources including books, articles and case studies were used to collect data related to theoretical foundations and extract primary factors and indicators. In inferential statistics, the questions were investigated using the system dynamics test and Vensim software. Based on the results obtained in the first cycle, the absence or lack of materials increases the project time and consequently increases the cost of the project. In the second cycle, the use of expert labor reduces the consultant's lack of correct estimation, which leads to the reduction of the employer's financial delays. In the third cycle, the delay in providing the plans increases the time of the project, which leads to an increase in the cost of the project. In the fourth cycle, the spread of Corona causes a decrease in the performance and productivity of employees, which results in a delay in the presentation of plans. In the fifth cycle, changing the technical specifications increases the delay in providing the plans, which increases the project time and, as a result, increases the cost of the project. As a result, the profit of the employer decreases and the employment of specialist labor also decreases. As a result of the consultant's lack of correct estimation, the increase and change of technical specifications will also increase.