Surface vortex and submerged vortex originating from intake wall often exist in fore-bay and sump in a large-scale pumping station. These vortices may affect the stability of pump operation. Because of big dimension, single diversion pier cannot effectively improve the intake flow field in large-scale pumping station. The Yonghu pumping station, a large-scale pumping station, which was located in Guangdong Province, was taken as the research object. The numerical simulation and the site test were performed in order to investigate the effects of combined diversion piers on rectifying intake flow pattern in fore-bay and sump. A new type of combined diversion pier composed of double-I type, three-I type and cross vortex baffle were proposed. The flow pattern, the vorticity and the uniformity of axial velocity distribution were compared between the original design and the optimized design. The numerical simulation results showed that the new type of combined diversion pier could effectively improve the intake flow field of the pumping station. For the original design, 2 large-size circulations in the fore-bay and submerged vortices in the sump were observed. The size and strength of vortices increased with the increase of the water depth. Furthermore, spiral vortices existed in the 2 sides of the sump. However, for the optimized design, the double-I type diversion piers in front reduced divergent angle of the fore-bay, and decreased the size and strength of surface vortex. The three-I type piers adjusted the uniformity of flow field, and water flow was well introduced to the corresponding pump sump. Submerged vortices originating from bottom wall were almost completely eliminated by the cross vortex baffle. Flow pattern was uniform and smooth in the inlet of pumps, and the streamlines of axial section of pumps were good, without vortices. The uniformity of axial velocity distribution of pump inlet section was as high as 91.42%, and the axial velocity angle approached 86.01°. Compared to the original design, the uniformity of axial velocity distribution of bell-mouth inlet and pump inlet section for the optimized design was raised by 7.8% and 10.6% respectively. The results of site test showed that the size and the strength of circulations and vortices were decreased observably. The peak-to-peak value of pressure fluctuation at the top of pump volute casing fell from 8.07 to 6.69 m, with a decrease of 17.1%. The vibration velocity RMS (root mean square) values of pumps before optimization almost were completely greater than 2.8 mm/s, namely the vibration level was at level D which was specified in the national standard methods of measuring and evaluating vibration of pumps, and in that level pumps could not normally work. After the combined diversion piers were installed, the vibration velocity RMS values of pumps were less than or equal to 2.8 mm/s, in other words, the vibration level was at level C, and the pumping station could operate normally. By numerical simulation and site test, it can be concluded that the combined diversion piers have many positive effects in rectifying intake flow field of large-scale pumping station. The research results provide a beneficial reference for hydraulic design of this kind of large-scale pumping station.