The country’s first full channel control system(TCC) established in Qingtongxia irrigation,in the control of Measurement and control one brake, non-steady non-uniform flow will appear in control weir when water distribution, in response to this phenomenon. In this paper, using the saint venant equations to simulate water levels and discharge In the process of weir adjustment,use the method of finite difference to discreting equations, use the Newton—raphson to solving nonlinear equations. The numerical calculation of the flow process for the U-shaped channel, Verification results show that the saint venant equations and Newton - posen iteration method is suitable for the measurement and control in one brake, the calculation results compared with the measured values, error is small. The results provide a basis for measurement and control one brake control mode