Pumped storage systems are attractive for power generation and storage with the development of clean energy. The combined operating mode of wind energy, solar energy and pumped storage systems is an emerging form of energy production, which brings pumped storage systems challenge in transient operation. Here we innovatively present a transient model of a multi-unit pumped storage system by coupling hydraulic system with unit system. We demonstrate that the proposed model can reflect the coupling effect of units during transient process. The simulation is provided with one unit shutdown under three kinds of closing laws and another unit controlled by PID controller at rated condition. The dynamic responses of unit-1 head are negatively related with its flow and output. The fluctuation of the unit-2 head is always higher than that of unit-1, and their fluctuation periods are similar. Analysis of dynamic characteristics of the pumped storage system suggest that transient performance improvement can be achieved by changing the motion law of guide vanes. The influence of guide vanes on the transient performance of the pumped storage system is investigated during load rejection process and the results could enable the flexible operation of multi-unit pumped storage systems for renewable power generation. (C) 2020 Elsevier Ltd. All rights reserved.