In order to analyze the effect of divisionpier on the discharge capacity of WES weir quantitatively, the discharge coefficient of a semicircular divisionpier under different water heads are studied by means of an experimental method in this paper, and the results are compared with those without divisionpier, the reasons for the decrease in discharge coefficient after setting up the divisionpier are analyzed by numerical simulation method. The results show that: the effect of divisionpier on discharge capacity can be reflected by the lateral contraction coefficient, there is little effect on the lateral contraction coefficient of the divisionpier with or without draining open channel in front of weir. The same is true of abutment pier. What's more, the lateral contraction coefficient is 0.969~0.978 under the experimental shape of this paper. Finally, the numerical simulation shows that the energy loss mainly occurs at the tail of the divisionpier.