In order to meet the double functions of irrigation and drainage and to save civil construction investment, dual-directional pumping system was adopted in the newly-built Zaogang pumping station, considering the large difference between the design and check head under the irrigation and drainage conditions. Under most of the irrigation conditions, the crest slab will not be submerged with free water surface. Based on the analysis on the design features of dual-directional inlet and outlet passages of Zaogang pumping station, the method of computational fluid dynamics was applied to perform numerical simulations on the internal flow of full passages including inlet and outlet passages，impeller, guide vanes, and gate slots, and the optimal hydraulic design of outlet conical pipe and the prediction of pumping system performance were conducted. The hydraulic losses of outlet passage and system efficiency were compared for different schemes and the design parameters of outlet conical pipe were optimized. Under the design conditions, the pumping system efficiency of the optimal scheme has reached 66.05%, which can improve the engineering benefits of Zaogang pumping station.