Abstract: The characteristics of ecosystem and sustainability have been ignored in safety evaluation for the plain reservoir. The plain reservoir has special characteristics such as large area, shallow water depth, long dam length and poor foundation treatment. On the basis of the health function regionalization, the comprehensive health assessment system for the plain reservoirs is established according to its safety, ecosystem characteristics, persistence, and other social， political and environmental factors. This index system includes 4 first-grade indexes, namely reservoir safety, social benefits, ecological effects and health persistence, and 15 second-grade indexes. In order to overcome the shortcomings of randomness and subjectivity in the traditional evaluation method and to eliminate the uncertainty during the evaluation process, a multi-objective and multi-layer fuzzy model for comprehensive health assessment of the plain reservoir is proposed, where the weight of each indicator is determined based on an improved analytic hierarchy process(AHP) method combined with fuzzy analysis of the relevant relationships of each indicator. The case history indicates that the research method is feasible and effective, and can be used widely in the reservoir health assessment. The analysis results obtained from this study are beneficial to the sustainable development and scientific management of the plain reservoirs