Abstract: In order to select efficient cellulose-degrading bacteria which can dissolve phosphorus and release potassium in tobacco stalk, 21 strains of cellulose-degrading bacteria were isolated from tobacco stalks. After determining their abilities to dissolve phosphorus and release potassium, comparing transparent circle diameter and colony diameter via Congo red staining, and determining the activities of carboxymethylcellulase and filter paper, a strain with high abilities to degrade cellulose, dissolve phosphorus and release potassium was selected. According to its morphology and molecular biology, the strain was identified as Bacillus subtilis and named as Bacillus subtilis SL-3A. The medium components and culture conditions were optimized by single-factor experiments, the results showed that the optimized cellulase production conditions for SL-3A were peptone as nitrogen source, carboxymethyl cellulose sodium as carbon source, C/N ratio 2 :1, inoculation volume fraction 8%, fermentation culture temperature 37 ℃, initial pH7, and fermentation speed 200 r/min. After the optimization of medium formulation and culture conditions, the CMCase and FPase reached 169.25 U and 44.99 U respectively. SL-3A strain degraded tobacco stalks by 20.85% after liquid fermentation for 15 days. In the preliminary experiment of tobacco stalk compost, the degradation rate of tobacco stalk crude fiber reached 34.62%, the effective phosphorus content increased by 0.13% and the effective potassium content increased by 2.12%.