Plant root system plays important role in soil erosion protection and affects hillslope hydrological process through infiltration.To quantitatively investigate root features of typical herb plants for hillslope protection in the Three Gorges Reservoir Region and their influence on soil infiltration,soil initial infiltration,average infiltration,stable infiltration and accumulative infiltration were measured on 4 typical hillslope protection herb plants,Vetiveria zizanioides(Lin.) Nash,Paspalum notatum Flugge,Cynodon dactylon(L) Pers.and Medicago sativa L.,ith bare land as a control.Soil samplers were used to take soil samples from the test area for laboratory experiments.Double-rings method was applied to make on-site measurement of soil infiltration.Root analysis system,WinRHIZOPro.2004c was used to characterize the root systems.The results indicated that:(1) Vetiveria zizanioides(Lin.) Nash and Medicago sativa L.had considerable higher root length density and root surface area density,as compared with paspalum notatum Flugge,Cynodon dactylon(L) Pers.(2) The soil infiltration rates were significantly amongst the different herb plants and at different soil layers under the same herb plants.The soil infiltration rates of soil under herb plants were significantly higher that of bare soil and declined with the increase in soil depth.The soil infiltration rates from high to low were in the order of Vetiveria zizanioides(Lin.) Nash,Medicago sativa L.,Paspalum notatum Flugge,Cynodon dactylon(L) Pers.(3) The initial,average and steady infiltration rates were 2.42,1.65 and 1.38 mm/min for Cynodon dactylon(L) Pers.,3.87,2.42 and 2.11 mm/min for Medicago sativa L.,4.84,3.37 and 3.00 mm/min for Vetiveria zizanioides(Lin.) Nash and 2.93,1.79 and 1.39 mm/min for Paspalum notatum Flugge and 1.31,0.86 and 0.71 mm/min for bare land respectively.(4) The soil initial,steady and average infiltration rates as well as cumulative infiltration were increased with increases in root length density and root surface area density,which were evidently correlated with root diameter from 0.50 to 5.00 mm.(5)Root length density and root surface density had significant impacts on Kostiakov′s model parameters,K and a.The K value,representing initial infiltration rate increased with increase in root length density and root surfer area density and the a value,representing the decrease rate of infiltration decreased with them.The K value from high to low were in the order of Vetiveria zizanioides(Lin.) Nash,Medicago sativa L.,Paspalum notatum Flugge,Cynodon dactylon(L) Pers.,Bare land.The K value and a value were 1.382 and 0.473 for Bare land,4.275 and 0.307 for Vetiveria zizanioides(Lin.) Nash,3.814 and 0.312 for Medicago sativa L,3.325 and 0.452 for Paspalum notatum Flugge and 2.742 and 0.404 for Cynodon dactylon(L) Pers.respectively.The results will be useful for hillslope vegetation protection and soil erosion control.