In order to investigate the influence of dividing pier on the hydraulic performance of a low-lift axial-flow pumping system，CFD method was used to simulate the three-dimensional internal flow of a low-lift pumping system with different outlet passages. The performance of the pumping system was estimated，and was compared with test data. Focusing on analyzing of the influence of dividing pier on the hydraulic performance of outlet passages and external characteristic of the pumping system, flows in two channels of the outlet passage are unequal to each other，the flow imbalance problem and the influence of velocity circulation on the hydraulic performance were analyzed as well. Results show that the dividing pier has great influence on the performance of the low-lift pumping system and should be avoided. Protrusive dividing pier makes the hydraulic loss of outlet passages increased and flow distribution more unequal. Backward extension of dividing pier does not influence the flow distribution, but makes hydraulic loss of outlet passage increase which induces degradation of the performance of the pumping system. Under the condition of zero velocity circulation, the hydraulic loss of outlet passage is in proportion to the square of flow, and the hydraulic loss is larger than that with velocity circulation and the flow is more complex. The internal and external performance of outlet passages has the relationship with the running condition of the pumping system，so it should avoid calculating the flow patterns of a separated outlet passage.