Flow characteristics of serial side weirs in a water distribution well under different inflow discharges were studied based on a 3D numerical simulation of turbulence, in which the free-surface was modeled by VOF method. The results show that evident difference of flow division characteristic exists between low and high discharges. Under low inflow discharge, the impact of adjacent side weirs is larger and the water lever along the distribution well centerline is little with relatively irregular unit discharge. Under high inflow discharge, the impact of adjacent side weirs is weak and the water lever along the distribution well centerline is a backwater curve. According to the characteristic of discharge coefficient, the side weir can be divided into two categories, and the relationship between the corresponding discharge coefficient and the relative head was established, which can be used to predict each weir’s discharge and the overall discharge diversion effect. This study can provide basis for engineering design, safe and efficient operation of water distribution wells in sewage treatment plants.