【Objective】Collapse of hills is a form of soil erosion widely distributed in South China. It occurs mainly in denudated granite hilly areas where vegetation has been destroyed. The collapses threaten the security of farmlands and residents, and cause huge economic losses. A typical collapsing hill contains five parts, that is, catchment slope, collapsed wall, colluvial deposits, gullies and alluvial fan. Colluvial deposits are poor in soil structure, posing the main source of erosion sediment in collapsing hills, weak in erosion resistance and very susceptible to runoff scouring. The traditional method of managing collapsing hills combines land leveling and planting of trees and grass. However, the method per disturbs the soil and besides, the benefits of revegetation come into being slowly. Soil particles in colluvial deposits are readily detachable with surface runoff. Now a new type of hydrophilic polyurethane, called W-OH, is available and good to intensify the cohesive force of soil particles between each other, and hence can be used to make up the weakness of the traditional method. 【Method】In this study a slope flume experiment was carried out to analyze effect of W-OH on soil detachment rate of colluvial deposits. The experiment was designed to have four W-OH concentrations, i.e. 2%, 3%, 4%, 5%, five slope gradients, i.e.8.8%, 17.6%, 26.8%, 36.4% and 46.6% and three flow rates, i.e.1.0 L s^-1, 2.0 L s^-1 and 3.0 L s^-1. The slope flume had a chamber to hold soil samples. Before the experiment, the soil samples were soaked in water for 12 hours to make the samples saturated and in the process of soaking, the water surface was kept slightly lower than the upper surface of the ring-knife. Slope gradient of the flume was regulated with a pulley system and water flow with a group of valves. Before the scouring process started, soil moisture content of the samples was measured, and soil detachment rate was calculated out of the difference between the soil samples before and after the experiment in dry weight. In order to facilitate the use of soil erosion models to estimate the effect of W-OH mitigating erosion, relationships of soil detachment rate with flow shear stress, stream power and unit stream power were analyzed. 【Result】Results show that as affected by a specific combination of slope gradient and flow rate, soil detachment rate decreased with the increasing concentration of W-OH. Such a trend was not obvious when the slope gradient was 8.8% and the flow rate 1.0 L s^-1 or 2.0 L s^-1。When the flume was over 8.8% in slope gradient, soil detachment rate displayed a clear gradient between the treatments and dropped by 1~3 orders of magnitude, as compared to CK, and the higher the W-OH application rate, the greater the descend gradient of the soil detachment rate. The analysis of relationships of soil detachment rate with hydraulic parameters shows that compared with CK, critical flow shear stress of the soil applied with W-OH increased. 【Conclusion】All the findings listed above indicate that the effect of W-OH reducing soil detachment rate is remarkable, and such an effect increases with increasing W-OH application rate. Under different circumstances, to reduce soil detachment rate decreases by two orders of magnitude, it is necessary to apply W-OH at a corresponding rate. Once W-OH is applied, a consolidated surface layer is formed with the surface soil of colluvial deposits, thus altering the process of soil erosion. When the consolidated surface layer is intact, soil erosion is very weak, and once the consolidated surface layer is ripped by surface runoff, soilerosion aggravates dramatically.