Abstract: To further study the hydraulic performances of bulb tubular pump and the rear guide vanes, computational fluid dynamics (CFD) method, RNG turbulence model and SIMPLIEC algorithm were used to conduct numerical simulation for the full flow passage of the pump. The flow patterns of the rear guide vanes and inner flow pattern of the pump were analyzed under four operation cases. The results show that the flow patterns are fine and there is no any back flow area in the pump and the guide vanes have well flow-guide effect under optimal operation; under low flow rate conditions, a large range of back flow and vortex appear at the pump impeller inlet, and disorder flow pattern is found at the impeller outlet, obvious recirculation areas appear around the blade-adjacent space, and also flow pattern at the rear guide vane manifest as turbulent and with a wide range of adverse flow area; in large flow rate condition, the flow pattern is well at the blade-adjacent area, and back flow is relatively rarely seen at the outlet, however the flow pattern around the guide vane is poor. In general, the rear guide vane has an obvious flow guide effect on the impeller outlet, and hydraulic loss is relatively large at the guide vane area when the pump diverges away from the optimal case.