The experimental study on the vibration characteristics of main feed water pump’s pressure pump in a China Pressurized Reactor 1000 (CPR1000) nuclear power plant is carried out. Using the vibration data acquisition equipment with high sampling rate, the vibration signals of electric feed water pump’s pressure pump at 50% load, 100% load and recirculation interlock start condition of the hot start are tested. It is found that during pressure rotor startup, the vibration increases rapidly and then decreased slowly to a steady abnormal value. The phenomenon is considered as a gradual changed forced vibration after synthesize the trend of vibration, the vibration frequency spectrum and axis of vibration. The duration lasts about 20 minutes. According to the structural characteristics of pressure pump rotor, a dynamics model of Jeffcott rotor with initial bending is established, by which the bending deformation and mass eccentricity are studied. The transient thermal bending of the pressure rotor during hot standby is considered as the main cause of the gradual change of vibration, which is verified by the measured thermal images of housing end. The test results illuminate the electric water pump’s vibration characteristics during the hot starting process, and it improves that delayed transient protection and stable operation protection of vibration values during hot starting process should be set separately.