Abstract: The seasonal change of water contained in soil and its effect on tree growth were studied in Jiulongshan,Beijing in 1984.Also,there was an analysis of relationship between tree growth and the yearly change of water stress.Based on the study,the conclusions were drawn that soil water has a violant change according to the seasonal and yearly distribution of precipitation,and that main factors causing the severe water deficit to tree growth are the unevenly seasonal and yearly distribution of the precipitation and the low water retention ability of the soil.