In domestic, there hasn't been specifically discussed about hydraulic calculation of thickener overflow launder in current literature. The basic hydraulic formulas were derived based on the theory of the Bernoulli energy equation and the steady gradually varied non-uniform flow in open channel. It also approximately calculated the depth of water in different locations along the way by using Runge-Kutta method. In such cases, the water surface profile can be simulated and appropriate section size and slope of overflow launder can be designed.