An equation of atomization quantity from energy dissipation by hydraulic jump was derived from dimensional analysis. Applying the Gauss diffusion equation, the spray diffusion in valley was studied under the conditions of continuous line source and random wind direction. Considering the spray-rain switching process, coagulation, condensation and evaporation of droplets, the authors calculated the air temperature, air relative humidity, spray density and the rainfall intensity in the lower reaches. The 3-D numerical results agree well with portotype monitoring data.