Guaranteed calculation for regulation (GCR) is indispensable in the operation of a pumped storage power station (PSPS), which aims to determine the rotational speed of turbines and pressure in the water diversion system under extreme conditions, such as load rejection. The closure law of guide vanes (CLGVs) requires optimization to minimize the maximum value of the water hammer pressure and the rotational speed in GCR. To address these two contradictory objectives, a multi-objective CLGV optimization (MOCLGVO) model is constructed in which these objectives are handled simultaneously. A recently proposed multi-objective artificial sheep algorithm (MOASA) is adopted to address the MOCLGVO problem. Thereafter, a recently proposed three-phase CLGV is adopted and compared with the traditional one- and two-phase CLGV in the GCR of a PSPS in China. According to a comparative study, the proposed three-phase CLGV optimized using MOASA achieves significant superiority over the traditional one- or two-phase CLGVs. (C) 2019 Elsevier Ltd. All rights reserved.