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In order to study the influence of impeller outlet span-wise circulation nonlinear distribution on external characteristics and internal flow field of the mixed flow pump in the inverse design, expand the optimization space, on the basis of the accuracy of numerical simulation verified by experiments, totally 17 different circulation distribution forms were constructed by inserting five control points into the span-wise of impeller exit to control the circulation distribution. Keeping other design parameters unchanged, the inverse design method was used to carry out three-dimensional modeling, and simulation calculation was carried out by commercial software CFX, the external characteristics and inner flow field were compared and analyzed. The results showed that the circulation distribution form had less influence of impeller efficiency on design points and small flow points. When the circulation value was small at the shroud and large at the 0.75ra, the pump efficiency under the condition of large flow would be greatly improved. In addition, compared with the circulation at the shroud, the circulation at 0.75ra played a leading role in improving the pump efficiency under the condition of large flow. The circulation distribution form had a greater impact on the cavitation performance of the impeller under every flow condition. The cavitation performance under small flow conditions and design flow conditions can be effectively improved when the circulation value was bigger at shroud and small at 0.75ra, but the cavitation performance under large flow conditions would be decreased accordingly. The circulation distribution form can significantly change the internal flow field of the impeller and affect the work capacity of the blade at different blade heights. Therefore, to further improve the comprehensive performance of mixed flow pump when using inverse design method, researching the nonlinear distribution of impeller outlet circulation had an important significance.