Abstract: From April to October of 2001, a mixed stand of Pinus tabulaeformis and Quercus variabilis which was 31 years old was observed to study rainfall and its redistribution through test plot in western mountain area of Beijing.The results showed that the rainfall mainly distributed in the growth season of trees, especially from June to August, which accounted above 80% of the total rainfall.The movement forms of every rainfall were all incomplete and the relation between rainfall and trunk flow and penetration flow was linear.When the rainfall was more than 1.43 mm, the stem flow appeared and when it was more than 0.4 mm, the penetration flow appeared.During experiment, the ratio compositor of three hefts in first distribution was:penetration flow (358.15 mm, 69.84% of total rainfall) >forest crown interception flow (138.05 mm, 26.92% of total rainfall) >stem flow (16.60 mm, 3.24% of total rainfall).In second distribution, the ratio compositor of three hefts was:the soil infiltration (223.08 mm) >dead wood and leaf interception (149.94 mm) >the earth's surface flow (1.73 mm).