The Grain for Green Project has changed hydrological processes on the Loess Plateau, but there is little information on the infiltration and runoff mechanism. Four typical land-use types (20a and 30a Robinia pseudoacacia woodland (20 or 30 RW), grassland (GL), and fallow slopeland (FL)) in the Caijiachuan watershed of the Loess area of western Shanxi Province were selected to investigate the effects of land uses on rainfall-infiltration-runoff processes under field simulated rainfalls.The dyeing tracer and image processing software were used to analyze the spatial distribution of preferential flows. The results showed that:(1) both the cumulative infiltration amount and the preferential flow distribution ranked the order:RW > GL > FL. The contribution ratio of preferential flow to total infiltration in RW was 2.5-4.5 times those of GL and FL. However, the contribution of preferential flow was less than 10% for all land uses and matrix flow dominated the infiltration processes. (2) The threshold depth in soil water impacted by rainfall infiltration was 60-70cm for the 4 land-use types. For all plots, antecedent precipitation evenly increased the soil water content of topsoil, while late precipitation increased the infiltration depth and its spatial variability in the increased soil water content. (3) The RW had significantly smaller surface runoff ratios to rainfall than GL and FL. Antecedent soil water content had little effect on the runoff in 20 RW plots, and had great influence on those in GL and FL plots. (4) The fine roots of diameter d<1mm significantly strengthened water infiltration and preferential flow occurrence, while roots of d>5mm had negative effect on infiltration and matrix flow. Antecedent water content, bulk density and clay content were the key soil factors hindering soil infiltration and the formation of preferential flow. These results indicate that the land-use types can change the processes of rainfall infiltration and soil moisture movement on the hillslopes, which may help understand the runoff generation mechanism.