Abstract: 【 Objective 】 To investigate the effects of different nitrogen fertilizer treatments on cotton stalk decomposition and soil physical and chemical properties. 【 Methods 】 The typical agricultural soil - grey desert soil in arid area was taken as the research object. Five nitrogen treatment levels (0 kg/hm²), low nitrogen (N₁: 112.5 kg/hm², N₂:225 kg/hm² ), medium nitrogen (N₃:450 kg/hm²), and high nitrogen (N₄:750 kg/hm²) were set in random block group with no straw addition and nitrogen fertilizer (CK) as the control. In the middle of October, 2019, the cotton straw was interrupted for 3-5 cm and put into 18 experimental plots with a medium returning quantity. The contents of cellulose, hemicellulosic, lignin, soil organic carbon, total nitrogen, pH and electrical conductivity of cotton stalk returned to the field were measured regularly during the decay of cotton stalk for one year. The evolvement characteristics of main components content of cotton straw and corresponding physical and chemical properties of soil were analyzed with the extension of decomposition time. 【 Results 】 Compared with nitrogen-free treatment, nitrogen-added treatment significantly reduced the lignin content of cotton stalk returned to the field in the early stage of decomposition (day 256), while cellulose and hemicellulose significantly decreased in the later stage, indicating that lignin was more sensitive to nitrogen fertilizer addition in the early stage of decomposition; In the early stage of cotton stalk decay, the organic carbon content of all soil treated with nitrogen increased significantly, but decreased in the late stage of decomposition. The organic carbon content of cotton stalk treated with low nitrogen (N₁ and N₂) was the highest. There was no significant difference in total nitrogen content between treatments. Nitrogen addition treatment significantly reduced the pH value and salinity of soil; Soil organic carbon content was negatively correlated with lignin and hemicellulosic content of cotton stalks (P<0.05, P<0.01). 【 Conclusion 】 Returning straw to the field and applying nitrogen fertilizer can accelerate the decomposition of cotton straw, while the low-nitrogen treatment (N₁ and N₂) can not only accelerate the degradation of straw, but also increase the content of soil organic carbon, so as to fertilize the soil.