The invention discloses a design method of a viscous mud-flow triangle base drainage canal optimum hydraulic section and the application thereof. The invention aims at the disadvantages in the prior art that the calculation method of the drainage canal optimum hydraulic section in the triangle base drainage canal design is complicated and no unique definite value can be obtained. The invention provides the design method of the viscous mud-flow triangle base drainage canal optimum hydraulic section. The method includes the following steps: calculating the size parameter F and the characteristic parameter S of the drainage canal optimum hydraulic section; then calculating the drainage canal hydraulic radius R; and finally the width W and the depth H of the optimum hydraulic section. The method is applicable to the control of the viscous mud-flow and coordinate use with other backbone type blocking projects. Compared with the prior art, the method can reasonably determine the shape and the size of the triangle base drainage canal optimum hydraulic section with unique definite value of the calculation result, effective, rapid and convenient calculation, thereby being applicable to the practical engineering.