Abstract: In order to effectively reduce the overall height of the straight pipe type vertical axial flow pump device, the outlet elbow is optimized. By taking a vertical axial flow pump device model as the research object, this paper designs a variety of schemes with the ratio of the turning radius and diameter of the outlet elbow as the characteristic parameter. The numerical simulation calculation of each scheme is carried out, and the optimal scheme is selected. The reliability of the numerical simulation results is verified by the model test. The numerical simulation results show that when the ratio of turning radius to diameter increases from 0.8 to 1.4, the efficiency of the pump device increases by about 3 %, the local head loss coefficient of the elbow decreases by about 0.3, and the pressure recovery coefficient of the outlet channel increases from 95.77 % to 96.54 %.If the outlet channel elevation is limited, it is recommended that the ratio of turning radius to diameter does not exceed 1.3. The hydraulic losses of guide vanes, elbows and outlet conduits interact with each other. Therefore, to further improve the efficiency of the pump device, the optimization of the outlet conduit should be optimized with the pump as a whole, and even the guide vanes and outlet conduits can be optimized together. At the same time, the local head loss coefficient of the elbow using one-dimensional theory under design conditions can accurately predict the hydraulic loss of the elbow.