Abstract: After the condensate pump of a 1 000 MW steam turbine generator set has been modified from frequency conversion,the vibration exceeds the standard in the frequency conversion speed range. After testing and analysis,the reason is due to the resonance of the motor shell structure and the excessive excitation force generated by the impeller. The vibration can be reduced to the excellent range by taking measures such as on-site dynamic balancing counterweight and reducing the exciting force of impeller.