In engineering projects, the engineering cost has special functions: first, the forecasting function. Engineering projects are often set up by large construction companies, and investors need to know and measure the investment projects in detail before construction. In this step, investors can budget the project cost as the basis for later decision-making, and also as the basis for construction enterprises to raise funds. Second, the control function, the project cost has the control function, on the one hand, it controls the investment decision of investors, on the other hand, it controls the cost of the project construction stage. The control function runs through all stages of the project cost. According to the repeated estimation and adjustment of each stage, the whole project is fully controlled. Third, the evaluation function, the project cost is an important basis for evaluating the total investment of investors. Project cost information is needed when evaluating the rationality of each project construction, investment benefit income, enterprise solvency, macro income and other factors. Fourth, the regulation function, the construction of large-scale engineering projects is directly related to the improvement of social public services, and has an important impact on national economic development, rational allocation of resources and capital flow. In any case, the state needs to carry out macro-control on engineering projects. Engineering cost plays an important role in adjustment.