Abstract: The yields, nutrient value and fermentation quality of two oat (Avena sativa) varieties and their effects on soil fertility of winter fallow fields were investigated to provide a theoretical basis for ensiling and processing of oats and further development of winter paddy fields. The four treatments of control A (fallow fields, no fertilizer), control B (fallow fields, with fertilizer), black oat treatment and yellow oat treatment were made in triplicate. There was no significant difference in hay yields, crude protein yields or relative feed value between the two oat varieties (P>0.05). Neither of the two oat varieties achieved a good fermentation quality under natural silage conditions, while adding lactic acid bacteria significantly increased the content of lactic acid and reduced pH, contents of butyric acid and ammonia-nitrogen of silages (P<0.05), thus markedly improving the fermentation quality. The contents of organic matter, total N and total K in winter paddy soil were significantly increased by cultivating oats. Planting yellow oats increased the contents of soil available P (P<0.05) to 36.66%, 31.75% and 18.03% higher than that of control A, control B and the black oat group, respectively. Planting black oat significantly (P<0.05) increased the activities of soil invertase and catalase which were 15.56% and 26.21% higher than that of control A, and 11.83% and 14.71% higher than that of control B. In summary, there is a great potential for cultivating oat in winter fallow fields, to not only produce large amounts of forages as silage material, but also to improve the soil nutrient and enzyme activities.