Based on the Navier-Stokes equations and the Spalart-Allmaras turbulence model, 3-D turbulent flow field in centrifugal pump with longmidshort blade complex impeller was calculated and analyzed numerically. The relative velocity and pressure distributions in the flowpart were obtained. It was found that the flow in the channel of the complex impeller was unsymmetrical due to the joint action between the volute and impeller. The flow in other channels was similar to that calculated using the single channel except for the ones near the volute throat. The backflow region was at inlet of longblade suction side, near middle part of longblade pressure side and outlet of shortblade suction side. The flow near volute throat was affected greatly by volute. The relative velocity was biggish and it was easy to bring back flow at outlet of the complex impeller near volute throat. And the static and total pressure rose uniformly from inlet to outlet in the impeller. The flow from the impeller outlet to volute had a trend to form the swirl near the wall of the volute and moved forward in spiral direction.