Abstract:Water quality of rainfall changes greatly after passing through trees canopy in the watershed. In this paper, an artificial pinus forest has been chosen to measure the precipitation inside and outside of forest, stemflow as well as the variations of their chemical contens. By analysing the characteristics of rainfall partitioning, the patterns of chemicals migrations in the field have been discussed.The results showed that the concentrations of TP, TN, Ca, Mg, Na and K were different among rainfall, throughfall and stemflow. In accordance with the rainfall partitioning, chemicals entered the field both as point source and area source, from which two different processes of motion were found. The chemical contributions in the field by rainfall and leaching from the tree was also discussed.