By using a dynamic experimental devices of debris flow，a series of indoor model tests on debris flow passing through drainage canal arc carried out. The shape of cross-section of modddrainage canal is rectangled with a width of 25 cm. The solid material is take from the Jiangjia ravine of which the gravel's maximum diameteris 40 mm. The test results are as follows:(1)Debris flow of the maximum diameter of<0.05mm can move on very small gradient of drainage canal;(2) The larger density of debris flow，the larger gradient of drainage is;(3) The gradient of moving debris flows in the drainge are relation with the density of debris flow，gravel s maximum diameter and fine particles.