The construction of a new power system requires to improve the response time of pumped storage units. In this paper， taking a specific pumped-storage unit as an example， systematical research is performed on the main differences of sequence control process and the variation law of unit stability parameters under normal and fast pumping to generating mode. Based on that， the in? verse-time vibration evaluation method is introduced to evaluate the impact of transition modes on the unit vibration peak-to-peak values. By analyzing the pressure fluctuation in the vaneless zone with the frequency spectrum analysis method， the phenomenon of hydraulic resonance in the vaneless region at low speed is found in generating rotation， and the correlation between resonance ampli? tude， frequency and speed is revealed. The research indicates that the mode transition from pumping to generate the fast transition is better than the normal transition. Compared with the braking method of electrical brake plus mechanical brake in normal transi? tion， the hydraulic braking mode under fast transition can significantly shorten the transition time from 438 s to 220 s. From the per? spective of vibration damage to the unit，13 of the 14 vibration and runout monitoring points prove that fast transition is conducive to prolong the expected life of the unit. Meanwhile， the fast transition is favorable to pass the hydraulic resonance occurring in vane? less zone at low speed. The hydraulic resonance time is reduced from 15 s in normal transition to 5 s in the fast transition， and the resonance speed range is compressed by more than 60%.