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Diffuser is one of the most critical flow components in submersible well pump, its hydraulic design has an important influence on the pump performance. A typical submersible well pump was chosen as the research object to study the influence of space diffuser vane number on the performance of submersible well pump by means of numerical simulation and experimental test methods. Based on the same curve profile, the diffuser vane number was adjusted to 6, 7, 8. The calculation domain was created based on single stage pump model, which was meshed with the high density of structured grids. Grid independence analysis was processed to determine the proper meshing scheme. The numerical simulations under multi-conditions were performed based on SST k—ω turbulence and standard wall function. Through the comparisons of predicted pump performance, it is found that the pump head is increasing with the increase of vane number under small flow rates. However, too many vanes occupy more passage area, which led to blockings and more hydraulic losses under larger flow rates. The scheme of 7 diffuser vanes matches the impeller very well, its import area tallies with the impeller outlet area and less hydraulic losses. The test results that this scheme has an pump performance, both the single-stage head and efficiency are higher than the national standard, which successfully completes the expected design goal. The head and power of numerical simulation prediction are slightly higher than the test results, the predicted pump efficiency is slightly higher than the test results, but the change trend is almost same with each other. The results of this study provide basis and reference for the improvement of submersible well pump performance.