Abstract: Based on the technical analysis on varing frequency and speed adjusting technique used in centrifugal pump sets of some tank farm, and calculation on the cost saved with the technique, the concept of Relative Energy Saving Rate(RESR)is put forward. The RESR characteristic curve and Power Reduction Rate (PRR) characteristic curve under different conditions of the pump set have been mapped on the basis of numerous calculation data. An analysis on the varing frequency and speed adjusting technique of pump set a nd its operating stability law are carried out, and the attention to be paid to the problems in applying the technique is given.