The improvement of the sill on the recirculation flow and the deflected flow downstream a unilaterally arranged pump-gateway was investigated based on a method combined numerical simulation of Flow-3D with physical model experiments. The effects of the size and location of the sill on the length and width of the recirculation flow and the velocity non-uniformity coefficient were studied, which can provide references for optimal design of the sill. The results show that the sill can suppress the recirculation flow and the deflected flow effectively, resulting in quick diffusion of the unilateral flow into the whole river width. The length and the width of the recirculation zone and the non-uniformity coefficient all decrease with the increase of both the height and adjacent distance of the piers, indicating a good rectification effect. With the increase of the sill width, the above parameters decrease at first and then increase, corresponding to better and non-significant rectification effect respectively. The variation trend of the velocity non-uniformity coefficients for all cases is similar in the flow direction, which increases at first and then decreases.