Analysis on shaft critical speed of pumped storage generator set is a complex problem in rotor dynamics under the influences of mechanical, electromagnetic and hydraulic factors. A 3D finite element model of a rotor bearing electromagnetic coupled system for pumped storage generator set was built in SAMCEF ROTOR. The stiffness coefficients of unbalanced magnetic pull, the shaft critical speeds and the modes of vibration were calculated. The effects of the stiffness change of unbalanced magnetic pull in generator, turbine guide bearing and generator guide bearings on the critical speed were also discussed. The results show that the unbalanced magnetic pull increases nonlinearly as the excitation current and rotor eccentricity increase, and decreases the first order lateral critical speed. The lateral critical speed increases with the stiffness of the guide bearings, among which the turbine guide bearing mainly affects the second order critical speed, while the upper and lower generator guide bearing mainly influence the first and third critical speeds.