Pot experiment was carried out to study the effect of the application of chemically pretreated rice straw (TS) on soil nitrogen supply and spinach growth and quality. After chemical pretreatment, the amount of cellulose, semi-cellulose and the silicon dioxide in TS was decreased, and the water-soluble substances increased. Application of TS with urea remarkably increased soil microbial biomass nitrogen and available nitrogen. Thus soil could supply the nitrogen to the spinach in a better synchronized way to the crop requirement. Compared with control, the application of the TS with urea (TS+N) increased the fresh weight of spinach per pot by 81.4% at the 41st day. The higher content of Vc and lower content of nitrate of the spinach was found in the treatment of TS+N than that in the treatment of single application. In conclusion, Crop straw could be better used in agriculture after it was pretreated in certain ways.