To study the influence of rainfall on preferential flow, a natural second Chinese pine (Pinus massoniana) forest in the granite region ofthe Three Gorges of the Yangtze River, which has not been greatly influenced bypeople, 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 sametime. 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 preferentialflow, such as preferential flow amount, preferential flow duration, delay timeto rainfall, peak values of preferential flow, were measured. The results showedthat the influence of rainfall on preferential flow was obvious. Fordischarge 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 rainfallamount. Valid regression equations were formulated between the factors of preferential flow and rainfall.