The invention discloses a method for designing hydraulic optimum section of V-shaped drainage canal for viscous debris flow inclined wall and application thereof. Aiming at the default that the hydraulic optimum section can not be determined because the section form and size of the V-shaped drainage canal of the inclined wall are generally designed based on personal experience in the prior art, the invention discloses the method for designing hydraulic optimum section of V-shaped drainage canal for viscous debris flow inclined wall. The method first calculates the hydraulic optimum section size parameter Beta for the drainage canal; then calculates the hydraulic optimum section characteristic parameter S; then calculates the corresponding hydraulic diameter R of the hydraulic optimum section for the drainage canal; and finally calculates the slope depth h1 and canal bottom depth h2 of the hydraulic optimum section. The method is suitable for the control of viscous debris flow and can be used matching with other mainstay block engineering. Compared with the prior art, The method of the invention can reasonably determine the shape and size of the hydraulic optimum section of V-shaped drainage canal of inclined wall to obtain maximum flow discharge ability, has effective, fast, and simple calculation methods, and is adapted to the requirement of practical engineering.