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The pressure pulsation in double-suction centrifugal pump is one of the key factors affecting the stability of pump unit operation. In order to reduce the pressure pulsation, the main causes of pressure pulsations in double-suction centrifugal pump were analyzed. The effects of blade loading curves on flow patterns in pumps were investigated. The relations between blade loading, blade outlet obliquity, staggered angle and the flow features including secondary flow and pressure pulsation were established. A new impeller design method with alternate loading was proposed. In the new design method, the main loading point on shroud located at the front of blade loading curve, and the main loading point on hub located at the rear of its curve. The impeller designed by this method was in the type of staggered arrangement in circumferential direction. The blade outlet edge was tilted forward, and the wrap angle difference between shroud and hub was very small. The field test on a large irrigation pumping station showed that the dominant frequency of pressure pulsations in the double-suction centrifugal pump designed by using this method was reduced significantly. The optimum efficiency and high-efficiency-range of the pump were also improved. This method could be used as a new approach to design/redesign double-suction centrifugal pumps with large power.