In order to evaluate the impact of shield tunnel construction on adjacent buildings, a method based on the fuzzy analytic hierarchy process (FAHP) and the interval number improvement technique for order preference by similarity to ideal solution (TOPSIS) is proposed. A risk assessment system based on soil properties, building factors, tunnel factors, shield tunneling parameters, and other factors is established after investigation. The FAHP is used to determine the weight of factors based on expert scoring. Based on the traditional TOPSIS method, 6 typical samples are selected according to the factor grading standard to determine the non-uniform risk rating criteria. For the first time, the interval improved TOPSIS method is applied to the risk assessment of shield tunneling beneath buildings. The engineering situation can be better represented by the interval number. Compared with traditional risk assessment methods, this method is more accurate, less affected by subjective factors, and more objective. The proposed method has been used to evaluate the risk of a certain masonry building, and the result is consistent with the actual situation, which proves its effectiveness of. Thus, the proposed method can provide reference for risk assessment of similar projects.