The system theory is applied to construct the BIM application project system project. Through the analysis of relationship among different variables, the stock flow graph is drawn to simulate and measure the economic benefits of BIM application in projects. The Vensim software is applied to draw the inventory flow graph and to test the model. According to the analysis on actual application of the project, the project data is extracted, and the Vensim software is applied to conduct simulation to obtain the benefit of BIM application in projects with more reasonable calculation process and more accurate calculation result. Influencing factors, including engineering cost, engineering error rate, engineering rework rate, working hours, working intensity, fatigue, management assistance, and etc., are all selected to compare and analyze the data of projects without applying BIM technology, and to analyze the impact of projects with BIM application, verifying the rationality and feasibility of the model.