To study the affecting factors of preferential flow, a 2.9 m-length, 2.6 m-depth soil profile was dug in Quxi watershed, Yangtze River. To analyze the influence of rainfall on preferential flow, the preferential flow process was observed when the rainfalls were recorded. And the soil physical and infiltration characteristics were measured to study their effect on preferential flow. The results showed that the rainfall amount that could cause preferential flow was more than 26 ram. The rainfall in the Three Gorges area can be divided into 4 types, namely gradually dropping raining, even raining, suddenly raining and peak raining. The preferential flow process was relevant to the raining process. With different rainfall types, the preferential flow appeared in different time, firstly in the peak raining, following in the suddenly raining, gradually dropping raining, and the even raining. The preferential flow would appear when the rainfall intensity was more than 0. 075 mm/min. In the studied area, the coarse soil particles increased with the soil depth, and for the deeper soil layer, its coarse particles were benefit to form preferential flow. The preferential flow accelerates the saturated infiltration rate of the soil layer 83 110 cm, and the quickly moving water in this layer also enhanced further formation and development of preferential flow.