The economic development in the eastern coastal area is rapid. The demand for cars increases and the demand for parking also increases. The above ground parking space is getting tight. The construction of underground garages can effectively alleviate this phenomenon. However, the air humidity in the eastern coastal area is relatively high, and the underground garages are prone to form the dew, which will cause the engineering quality defects and economic losses. To solve this problem, the dewing phenomenon in underground garages of typical regional projects is analyzed. Several causes of dewing are given. The dewing may cause a series of hazards to the project. Some targeted measures to prevent and control the dewing are proposed, which provides the decision-making reference for the design units and construction and operation units in the process of engineering construction and operation.