Abstract: Adjusting the opening of the control gate is significant for controlling the water level and achieving reasonable water delivery. In this paper,the flow characteristics of the control gate and rectangular diversion are tested at different flow and different gate openings in trapezoidal channels,hydraulic elements of the water diversion and the upstream and downstream are observed such as water depth,flow velocity,and the variation of water surface along the main channel is measured. In addition,the relationship between flow coefficient and gate opening and water depth in front of the gate is established based on dimensional analysis. The results show that at different discharges,the water depth along the trapezoidal main canal has the same variation pattern,and the overall trend is decreasing first,then increasing and decreasing,and a backwater is formed at the downstream of the control gate. Under the condition of free outflow,when the inflow flow is25.35,28.93,32.38,35.50,39.70 L/s respectively. The critical value of gate flow and weir flow appear when the gate opening is 11,11.6,12,13,14 cm. The range of relative gate opening（e/h）is 0.792,0.798,0.808,0.819,0.823. It is different from the theoretical value（0.6）. The boundary between weir flow and gate flow is not a fixed value,and there is a certain gap between critical value and theoretical value. The critical value is affected by the channel shape,gate pier shape,flow rate and other factors. On the other hand,it is found that the flow coefficient（m）in the side channel flow formula is related to Froude number and relative gate opening（e/h）based on the dimensionless principle. The flow coefficient（m）decreases with the increase in the Froude number and relative gate opening（e/h）under different flow rates,but the relative gate opening has a greater influence on the flow coefficient than the Froude number. The flow coefficient is approximately inversely proportional to the Froude number under different discharges. The flow coefficient（m）relation with relative and gate opening（e）and water depth in front of the gate（h）is obtained,and the average error is 0.73%. The diversion flow ratio decreases with the increase in the relative gate opening at different discharges. In the case of large flow,the diverging ratio tends to change greatly,and the maximum decrease is 16.78%,which means that the gate opening has little influence on the split ratio at a small discharge. This study is of great significance to guide rational water allocation and control in irrigated areas.