Abstract: In order to solve the evaluation and decision making problem of reservoir multi-objective operation schemes, a new evaluation model based on regret theory(RT), grey target theory(GT) and maximum entropy theory(MET) was constructed and named as RT-GT-MET. Firstly, the decision makers' regret aversion psychology and risk preference attitude was considered based on RT, then the happy and regret function based on positive and negative ideal points were separately formed. Secondly, by determining the positive and negative target distance with GT, the space projection distance to the positive and negative target was used to establish the comprehensive target distance function. Then, MET was introduced to reduce the uncertainty of evaluation process, and a nonlinear optimization model with the minimum comprehensive target distance and the maximum weight entropy was established. Finally, the model was optimized efficiently within the search range determined by the subjective and objective weights, and the decision order was made according to the optimal comprehensive target distance. The two application results verified the rationality and applicability of RT-GT-MET, and indicate that it is able to improve the simplicity, scientificity and practicability of multi-objective decision making, so as to provide an effective new idea for decision making of reservoir multi-objective operation.