As a result of soil forming process and human activities,rock fragments or detritus exist in soils,different in contents and sizes.Their presence does have some effects on some physical properties of the soil as well as water infiltration process.Based on the experiment of vertical infiltration in lab,effects of content of rock fragments (0%,10%,20%,30%,40%,50% and 60%) and size of the detritus(0.2～0.5cm,0.5～1.0 cm,1.0～3.0 cm and 3.0～4.0 cm) on water infiltration were studied.The purpose of this study is to determine effect of rock fragments different in content and size on water infiltration process and find out its mechanisms.