In order to investigate the effect of adjustable outlet guide vane on hydraulic performance of axial-flow pumping system, the pumping system with seven different adjustable angles of outlet guide vane were simulated based on the RNG k—εturbulent model and Reynolds time-averaged equations. Vectorgraph of airfoil flow were analyzed under different operating conditions at different adjustable angles of guide vane. BP-ANN prediction model about effect of adjustable outlet guide vane on the hydraulic performance of axial-flow pumping system was established based on numerical results. The effectiveness of prediction model was verified by using theoretical analysis and numerical simulation. The results showed that the high-efficiency area moved to the large flow rate direction with the adjustable angle of guide vane increased along clockwise, otherwise, it moved to the small flow rate direction. The internal flow field of guide vane was improved by adjusting angle and the flow separation of tail and guide vane inlet ledge were decreased or eliminated, which would improve hydraulic efficiency of pumping system. The input model of the BP-ANN prediction model is presented and the number of middle layer is fixed by many tests. The characteristic data of 42 pumping system operating conditions are used to train the network model, and the data of the other seven pumping system operating conditions are used to test the network model. The prediction accuracy of BP-ANN model was below 1%, which can meet the requirement of practical engineering.