Abstract: In order to study the finger flow phenomenon during ponded infiltration process in layered soil, an experimental study was carried out to observe the occurrence, mechanism and environment of finger flow in six soil columns which have different grain sized sands overlain by loess soil. The results show that the main factors for finger flow occurrence are the stable infiltration rate and the saturated hydraulic conductivity of the sand layer. The ratio of infiltration rate to hydraulic conductivity can be used as an important quantitative index for occurring finger flow. The critical value for finger flow occurrence is the specific value <0.02, that is to say, when the infiltration rate of sand layer approaches 1/50 less of the saturated hydraulic conductivity, finger flow occurs.