Reinforcement of dangerous reservoirs is a huge project in China, but the theories and methods of comprehensive assessment for the reinforcement effects are limited, leading to the difficulty to accurately evaluate the actual effects for a large number of reinforcement projects. The quantitative analysis of the evaluation method of the reinforcement effect for dangerous reservoirs is studied. Four reinforcement impact factors are defined, including the evaluation of reinforcing schemes, functional index rehabilitation, engineering construction and the benefit of reinforcement, based on which a “Building Block Model” of the influence factors is established to evaluate reservoir reinforcement effect. Quantification methods for the reinforcement effect evaluation indexes are proposed, including the evaluation indicator grading, time-dependent and time-independent evaluation indexes, subjective and objective weight of experts, static and dynamic weight. The quantitative evaluation model for evaluating the reinforcement effect of dangerous reservoirs is obtained. The model is applied to the reinforcement assessment of a dangerous reservoir and the results agree well with the actual situation and the acceptance conclusion.