The influence of cotton straw returning and soil decomposition and soil characteristics were studied. With different length of cotton straw as the research object, used the design (CK) as the control, the cotton straw about 3 cm, 6 cm, 10 cm, buried in 0 cm length, in early June 2023,10 cm, 20~30 cm soil layer, cellulose, hemicellulose, lignin, C, N, P, K content, soil pH, water content, salt content, organic matter, total nitrogen, quick phosphorus and quick potassium content. Analyze the changes in the decomposition amount, chemical composition, nutrient content and soil physical and chemical characteristics over time. Cotton straw rot rate are first fast after slow, until tend to stop, 3 cm long cotton straw in 10~20 cm and 20~30 cm deep soil rot effect than 0~10 cm soil, cotton straw chemical composition and nutrient content decreased over time, cotton straw returning significantly increased the soil organic matter, phosphorus and potassium content, the soil nitrogen content is not significant under various conditions. Straw returning to the field can improve the soil organic matter content through the release of nutrient content, and then improve the ability of fertilizer supply and fertilizer preservation of the land.