In this study, after identifying the factors and parameters affecting the duration of construction projects, the system thinking approach and system dynamics method are used to find the root causes, relationships and feedback between the factors. Library studies were used to identify the factors affecting the duration of the projects and Delphi interviews with 22 experts were used to improve and supplement these factors. Then, a conceptual model based on causal loops is presented to better understanding of the relationships between variables. Afterwards, using the approach governing the system dynamics method, a flow diagram is compiled to better understand and learn and also to more dynamic analysis of the research problem. The accuracy of the accumulation flow model has been measured with some tests, including reviewing and evaluating the behavior and structure of the model, and also four main scenarios were formulated for implementing different executive policies. Based on the results, the behavior and performance of the model have been evaluated and analyzed. The results obtained from the evaluations confirm the correct performance of the proposed model. Simulation results across four scenarios demonstrated that the most effective levers for project acceleration are the minimization of owner-driven scope/method changes and the strategic investment in human resource development (training and fair compensation), which significantly mitigate project delays by improving system efficiency. It is hoped that the understanding gained from this learning system will provide the necessary basis for making better and more efficient decisions in the field of project time.