The overpressure and overspeed of pump-turbines are common consequences of interaction between pumped storage power plants and intermittent sources of energy. In this paper, by analyzing the S-shaped zone of characteristic curves, the transient operation of Siah Bishe pumped storage power plant during the full load rejection of the unit is numerically simulated. In this way, the second version of non-dominated sorting genetic algorithm (NSGA-II) is applied to perform a multi-objective optimization. The optimization processes of wicket-gates closing law and the surge tank position are carried out to minimize the maximum overpressure and the pump-turbine overspeed. Optimization results in Case 1 show that by optimizing the four-slope closing law of wicket-gates and placing the surge tank closer to the upstream reservoir (by 86.8 m), the maximum overpressure and the pump-turbine overspeed decrease by 4.2% and 7.1%, respectively. Also, the maximum rise and fall in the water level of surge tank decrease by 5.2% and 7%, respectively. Optimization results in case 2 reveal that an uncomplicated closing law with only two optimized strokes can be a proper substitute for the original four-stroke closing law, leading to a remarkable decrease in the pump-turbine overspeed (6.4%) and 2.5% reduction in the maximum overpressure. (C) 2019 Elsevier Ltd. All rights reserved.