Abstract:The triangular,trapezoid,rectangular and circular transects are applied as debris flow drainage canal widely at present. The section factor coefficient is defined as the ratio of wet perimeter and hydraulic radius,and the section factor coefficients of four kinds of debris flow drainage canals(triangle,trapezoid,rectangle and rotundity) are deduced.When the bed slope coefficient of triangular drainage canal is greater than 0 and less than 3,with the bed slope coefficient increasing,the hydraulic condition is more advantageous. And while the bed slope coefficient is greater than 3,the hydraulic condition become disadvantageous. The hydraulic condition of debris flow drainage canal is best as the bed slope coefficient is equal to 3. When the bed slope coefficient of trapezoid drainage canal is greater than 0 and less than 0.577,with the bed slope coefficient increasing,the hydraulic condition is more advantageous. While the bed slope coefficient is greater than 0.577,the hydraulic condition become disadvantageous,and the hydraulic condition of debris flow drainage canal is best as the bed slope coefficient is equal to 0.577. The hydraulic condition of circular section is best among four kinds of drainage canals. when the bed slope coefficient of trapezoid is greater than 0 and less than 1.333,the hydraulic condition of trapezoid section is better than rectangular section,and when the bed slope coefficient excesses 1.333,the rectangular section is better than the trapezoid section;when the bed slope coefficient of triangular is greater than 0 and less than 0.75,the hydraulic condition of the rectangular section is better than that of the triangular section,as the bed slope coefficient excesses 0.75,the triangular section is better. Under the same bed slope coefficient condition,the trapezoid section is better than the triangular one. When the bed slope coefficient is among 0 and 1,and the bed slope coefficient is 1,the hydraulic condition is the same.