Abstract: In order to clarify the mineralization characteristics and nutrient release rules of decomposed cow dung in hilly tobacco fields in northeastern Yunnan, taking the tobacco-planting soil in Qujing tobacco-growing area as the research object, the in-situ cultivation method of nylon mesh bag field was used in 2023 to study the mineralization characteristics of organic carbon and nitrogen and the effect of soil fertilization during the growth period of flue-cured tobacco after the application of decomposed cow manure into the soil. Results showed as the follows (1) After burying the decomposed cow dung, the mineralization rate of organic carbon was fast in the early stage (0-80 d), and the amount of organic carbon mineralization accounted for 93.49 % of the cumulative mineralization during the study period when buried for 80 d. The mineralization rate of organic nitrogen was low from 0 to 20 days, and it was fast after 20 days. The amount of organic nitrogen mineralization at 80 d accounted for 91.92 % of the cumulative mineralization during the study period. After 80 days of burial, the mineralization rates of organic carbon and nitrogen tended to be stable. (2) Forsoil inorganic nitrogen, the content of nitrate nitrogen is much higher than that of ammonium nitrogen. The contents of nitrate nitrogen and inorganic nitrogen were low at 0-40 d after burial, and then increased rapidly. The content of decomposed cow dung treatment was always much higher than that of the control treatment. The content of ammonium nitrogen was the highest in 0-10 d after burial, then decreased rapidly, and increased slowly after 60 d. The content of ammonium nitrogen in cow dung treatment was higher than that in control and the fluctuation range was larger. (3) The contents of soil inorganic nitrogen, available phosphorus, available potassium, humic acid, humic acid and fulvic acid were significantly higher than those of the control. (4) After 30 days of decomposed cow dung application, the soil Hu/Fu ratio increased and the degree of humification deepened, which significantly increased by 29.85% compared with the control at 100 days after burial. In general, the application of decomposed cow dung can effectively increase the soil nitrogen content, promote the accumulation of soil humic acid components, and significantly improve the soil quality in the hilly tobacco fields of northeastern Yunnan. Considering the law of carbon and nitrogen mineralization of decomposed cow dung and the demand law of flue-cured tobacco, it can be applied 30 days before tobacco seedling transplanting to meet the fertilizer requirement law of flue-cured tobacco 'less when rich and old when poor’.