Determining initiation stage to regulate the plant growth and soil water is the base of sustainable use of soil water resources. In this paper, the dynamics of soil water were continuously measured with a neutron probe in fixed positions in the wasteland and newly sowing Caragana forest land during the period from 2002 to 2006 and the data measured was analysed. The results shows that the depth plant use soil water increases from the surface soil on 24th June to 220cm in the first year，and that the depth plant absorb and use soil water and soil water consumption increases，and the amount of soil water storage reduced with increasing age apart from the wet year in 2003 in which the amount of soil water storage increased by 122.8 mm at the 2\|year\|old Caragana forest land. It is also discovered that the soil water content at the soil layer of 100 cm is smaller than the wilting coefficient in the 3\|year\|old Caragana land and dried layer of soil become more and more serious in 4\|year\|old Caragana land and the initiation stage of regulating the relationship between Caragana growth and soil water is 5 years. Effective measures should be taken to control plant density and growth in order to realize sustainable use of soil water resources.