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Double suction centrifugal pump has characteristics of large flow rate and high head. It is widely used in agricultural irrigation and water delivery and other projects. The volute and the impeller in double suction pump have rotor-stator interaction. The match between the two will have an impact on the hydraulic performance of double suction centrifugal pump. Therefore, it is very important to study the matching relationship between the volute and the impeller. The CFD numerical simulation was combined with the experimental data. By studying the impact on the hydraulic performance with different specific speeds, the optimal volute area ratio and its regular pattern were obtained. The findings were as follows: when the volute area ratio was increased, the maximum efficiency point was shifted to the large flow rate. The head and efficiency were decreased, and the average efficiency of the high efficiency area was reduced. When the area ratio was reduced, the head and efficiency were increased in a certain range, and the maximum efficiency point was moved to the small flow condition. However, when it was reduced to a certain extent, the head and efficiency showed a rapid decline. Finally, based on the summary of the optimal volute area ratio of the double suction pump with different specific speeds, it was found that with the increase of the specific speed, the optimal volute area ratio was increased, and the range of the high efficiency area was widened gradually. The results provided a reference for the reasonable selection of the volute area ratio in double suction centrifugal pump and improved the hydraulic performance of double suction pump.