Abstract: To study the influence of rainfall on preferential flow, a natural second Chinese pine (Pinus massoniana) forest in the granite region of the Three Gorges of the Yangtze River, which has not been greatly influenced by people, was selected as an experiment site. The process of preferential flow was recorded by an automatic flowmeter. The process of rainfall was recorded at the same time. The five factors of rainfall, including rainfall amount, rainfall duration, ante-precipitation, rainfall amount whose intensity exceeds 20 mm/h and peak values of rainfall intensity, were measured. The four factors of preferential flow, such as preferential flow amount, preferential flow duration, delay time to rainfall, peak values of preferential flow, were measured. The results showed that the influence of rainfall on preferential flow was obvious. For discharge of preferential flow, the decisive factor was rainfall amount. For duration of preferential flow, the decisive factors were rainfall duration and rainfall amount. For peak value of preferential flow, the decisive factor was rainfall amount. Valid regression equations were formulated between the factors of preferential flow and rainfall.