Abstract: In order to improve the numerical simulation accuracy of the nuclear main pump at all the working points, three factors affecting the numerical simulation results, i.e., the near-wall mesh scale, turbulence model and flow state are comprehensively studied. The results show that the RNG k-ε turbulence model and the standard wall function method have higher calculation accuracy when y⁺=50, and the calculation accuracy is also higher than that of three kinds of turbulence models, i.e.,  the RNG k-ε enhanced wall function method, low Reynolds number k-ε and SST k-ω. However, the calculation results of the above-mentioned different grid scales and turbulence models have large errors. Under the unsteady state calculation, the calculation accuracy of the unsteady state calculation method is significantly improved compared with the steady state calculation method, which can reflect the hump phenomenon of the head curve near the dead point, and the calculation accuracy of efficiency is also improved. The unsteady calculation method is more suitable for performance prediction of nuclear main pump.