Abstract The calculation of large oscillation transition process is of great significance for pumped storage power station, which is beneficial for ensuring the safe of the power station and extending the lifespan of the unit. Due to the presence of inertia in water and rotating components of the unit, as well as energy imbalance in the system, hydraulic transients will cause drastic changes in water pressure in the waterway system and unit speed, resulting in a sharp increase or decrease in pressure and a sharp change in unit speed, endangering the operational safety of the power plant and affecting the lifespan of the unit. It is necessary to optimize the layout of water conveyance system, basic parameters of units, and the closing law of guide vanes through calculation and analysis of large oscillation transition processes. Relying on a pumped storage power station in Guizhou, this paper analysis the sensitivity of the factors affecting the calculation results of the large oscillation transition process, such as runner characteristics, guide vane closing law, moment of inertia GD2, surge chamber diameter and restricted orifice size, to provide reference for similar projects.