Abstract: In order to study on the flow loss characteristics of axial-flow pumping system and fatigue reliability of impeller,the steady three-dimensional numerical simulation was carried out to simulate the internal flow of axial-flow pumping system,which was analyzed by the entropy production theory further.When nD is fixed value,stress and strains of different size impellers were analyzed based on fluid-structure coupling methods.The fatigue reliability of the impeller was predicted according to the Palmgren-Miner theory.The results show that the flow loss in the axial-flow pumping system is mainly related to the entropy production in the turbulent flow.The turbulent dissipation is significantly larger than the direct dissipation no matter in the inlet and outlet conduits or in the guide vane.The turbulent dissipation of guide vane is maximum in all flow domains of axial-flow pumping system.With the increase of impeller diameter,the maximum stress and the maximum strain are gradually decrease.The maximum stress is in the leaf root of blade,and the maximum strain is at the edge of inlet side under different operating conditions.With the increase of impeller diameter,the minimum of fatigue safety factor is gradually increases.It suggests that nD is fixed value,the diameter of impeller should be appropriately increases,and the rotational speed of the impeller should be reduced,according to the fatigue safety factor of impeller.