Abstract: Based on three years point-fixed observation,this paper analyzed the relationship between water supply and consumption of black locust(Robinia pseudoscacia L.)and Chinese pine(Pinus tabulaeformis Carr.),the main tree species of protection forests in the loess area of the western Shanxi Province.In April,May and June,the water supply was less than water consumption,while in raining season,the water supply was abundant,and the water storage in soil was increased. During dry seasons and years, more water consumption and less available water supply occurred in high-density stand,showing a serious water deficiency. The water deficiency was in order of south-facing slope>semi-south-facing slope>north-facing slope.The study shows that water consumption characters coefficient could be used as an index to indicate the growth pattern of trees,and the relationship between water supply and consumption.