Preliminary design is to further refine each sub-project on the basis of feasibility study, which is the basis of construction drawing design and construction organization design. At the same time, in the preliminary design, the project budget is one of the main basis for investment. Of course, the construction needs to be further refined and the investment needs to be further verified, but the total investment should not exceed the preliminary design budget unless there are many changes. Therefore, the preliminary design is still very important, playing the role of a bridge, between feasibility study and construction design.