Abstract: In order to solve the low-frequency vibration problem of the vertical condensate pump of the thermal power plant and ensure the safe operation of the unit, the method of on-site vibration test combined with finite element analysis was adopted to confirm the cause of the failure. Through on-site vibration test and analysis, it is confirmed that the low-frequency vibration is caused by the resonance of the motor shell structure, and combined with the three-dimensional modeling finite element analysis, it is found that the source of the excitation force is the resonance of the outlet cylinder excited by the water flow. By designing a reasonable natural frequency change scheme of the outlet cylinder, the low-frequency vibration problem of this type of condensate pump is effectively solved.