Abstract: Abstract: Usually, centrifugal pumps run under steady working conditions, i.e. the pump rotational speed or its working point is basically steady or changes slowly in a long period of time during operation. Hereby the existing investigations into the performance of centrifugal pumps are mainly limited to the steady operating conditions. However, with the expansion of centrifugal pump applications and the increasing complexity of fluid flow systems, centrifugal pumps need to be operated in transient operating conditions, such as startup, stopping and rapid change of rotational speed etc. These transient operational conditions can result in a few remarked negative effects on electric grids and pipelines related. For example, the abrupt startup of a large-scale pump in pumping stations can cause a considerable impact on a local electric grid and induce a pressure surge in the pipeline. Nonetheless, the transient hydraulic characteristics of a centrifugal pump are very important to the safe and reliable operation of a pumping system. Furthermore, a full understanding of transient hydraulic performance of a centrifugal pump can be helpful for the optimization of pump hydraulic design and the enhancement of its reliability. As such, studying the pump hydraulic performance during transient operating periods has become a more necessary and urgent technical issue, and has drawn significant attention in the past 30 years. On one hand, centrifugal pumps with closed-type compound impeller of long and short vanes in a low specific-speed and high head are extensively used to transport a variety of liquid and are indispensable liquid conveying equipment in aerospace, petrochemical, automobile industries and other important sectors. On the other hand, however, the existing investigations are mainly associated with centrifugal pumps with closed-type ordinary impeller. In this paper, the transient performance of the centrifugal pump with a specific-speed of 45 and compound impeller was measured to reveal the transient characteristics of a low specific-speed centrifugal pump with closed-type compound impeller during stopping period due to power outage. The time-history profiles of performance parameters were obtained, such as rotational speed, static pressures at the pump inlet and outlet, pump head, flow rate, torque and shaft power at eight flow rate ratios where a stopping period starts to occur. As a reference, the transient performance of the centrifugal pump with ordinary impeller in the same specific-speed and dimensions and blade shape was tested as well. The experimental results showed that the time for the impeller stopping rotation was shorter and shorter, and the rotating speed curves become steeper with increasing flow rate ratio. Interestingly, the rotational speed time-history curves can be fitted quite well with a 4th-order polynomial function. In the initial period, the instant flow rate curve was kept constant basically. With increasing flow rate ratio, the period was extended slightly, but the time at the instant flow rate zero became longer. This behavior was completely different from that of the instant rotational speed curves. The instant pump head and outlet pressure exhibited a similar pattern as the rotational speed curves. Even though the inlet static pressure varied considerably during the stopping period, it gradually became relatively stable at about 6 s. Once again, the instant torque and shaft-power curves shared nearly identical profiles with the rotational speed. The length of characteristic time of performance parameters got longer with increasing flow rate ratio. At a flow rate ratio, the length of characteristic time of performance parameters was in the following order from the longest to the shortest: flow rate, head, rotational speed, torque and shaft-power; further, the length of characteristic time of the centrifugal pump with compound impeller was extended in comparison with the pump with ordinary impeller, especially for flow rate, head and rotational speed.