The key indexes commonly used to express characteristics of reservoir operation performance during drought are described，and their practical formulas, which are easy to deal with for computation procedure, are prposed. The structural form of multi -  objective mixed -  integer programming model is established based on the principle of maximum reliability, most resilience, and minimum vulnerability of reservoir water supply. In the application of model, the weight method is employed to solve multi -  objective decision problem. According to impacts of various  weights of objective on model results, the characteristics of two kinds of    objective functions and their decision -  making process are compared. The virtues and shortcomings of both objective function structures are  pointed out for evaluating reservoir operation performance.