The dynamics of soil water content under different tillage systems were studied throughout the growing period of oat (Avena sativa L.). The treatments included tillage (zero tillage, sub-soiling, and moldboard plow), residue cover (with and without mulch), and crop rotation (continuous cropping and crop rotation). The results indicated that soil water content and crop water use efficiency was improved under zero tillage with mulch. When crop residue was removed, soil water content under zero tillage was reduced, especially in the surface layer. Comparing to the moldboard plow, sub-soiling increased soil water content and storage, either with mulch or without mulch. For all the three tillage treatments, soil water content with mulch was significantly higher than that of without mulch. Furthermore, soil water content and crop water use efficiency under crop rotation was consistently higher than the continuous cropping. We concluded that sub-soiling with mulch was the optimum management system in this area. At present, however, a combination of crop rotation and sub-soiling is a viable option, since there is not enough crop residue available for mulching.