Research conclusions: Because of the distortion of cost calculation，the economical estimate results of same proposal are inconsistent with different principal parts. Introduction of the investment decision-marking theory can forecast truly the present value of engineering cost in the engineering proposal. The opportunity cost analysis theory is used for reflecting really the value of ”the land resources assets” consumed in the project. The total expenses of engineering proposal during the whole alternative period must be considered and the dynamic engineering cost calculation method is adopted to accurately reflect the real cost of engineering.