In order to study the internal flow characteristics in the flow passage components of flow-ejecting centrifugal pump under off-design conditions, the type JETST-100 self-priming pump was selected. It consists of seven parts: the inlet pipeline, jet aerator, wear ring, elbow, impeller, outlet pipeline and pump chamber. The transient numerical simulation for internal flow situation of computational model was carried out based on RNG k-ε turbulence model by using CFX software. The flowing information of velocity and pressure in flow passage components of centrifugal pump were obtained. Comparison of flow change between inlet and throat of jet aerator under different operating conditions was performed and the simulation results were compared with the test results. The results showed that the highest pressure area of jet aerator was located at the inlet of nozzle, low pressure area was located at the vicinity of throat, and the maximum velocity occurred at the area of the vicinity of nozzle, the minimum velocity generated at the inflow part of suction liquid. With the flow rate decreased, mass flow rate of reverse flow in throat of jet aerator was increased; effluent liquid from the impeller was mostly reversed to the inlet of jet aerator. The flowing analysis of impeller showed that the blade suction surface velocity was generally higher than the blade pressure surface velocity, which further affected the operating efficiency of the pump. The study results will supply a theoretical reference for hydraulic optimization design of the internal flow status of flow-ejecting centrifugal pump under off-design conditions.