Based on the field surface shallow flow experiments,the roughness coefficient value (n)on different land have been quantitatively demonstrated by changed Manning Formula in this pa-per.The result shows that the relationship of roughness coefficeint value(n)to litter and grassamount appears to be an orthographic correlation on forest land.And the order of roughness coeffi-cient value (n) from lower to higher on different condition of land use is as follows:soil road,cultur-ing land,walnut plantation,the land of artificial locust forest,the land of shrub forestry and theland of artificial Chinese pine forest.This paper deals also with the relationship between roughnesscoefficent value(n)and the infiltration of water.the preliminary result shows that the higher theroughness coefficient value (n) is,the more the infiltration of water will be.