To investigate the effects of combined application of rapeseed-cake and decomposing agent under the condition of rapeseed straw returning on the rhizosphere soil microenvironment and the yield and quality of flue-cured tobacco, this study took the “rapeseed-tobacco” closed-loop cultivation mode in Luoping County as the research object, conducted a field experiment, and compared and analyzed the regulatory effects of different treatments on soil physicochemical properties, enzyme activities, bacterial community structure, as well as tobacco economic traits and the quality of upper tobacco leaves. The results showed that, compared with the control, the treatments with rapeseed-cake and decomposing agent significantly improved soil fertility. Specifically, soil organic matter, alkali-hydrolyzable nitrogen, available phosphorus, available potassium, and cation exchange capacity (CEC) increased by 4.6%-13.7%, 3.2%-12.9%, 4.0%-18.1%, 10.7%-57.9%, and 3.9%-16.5%, and pH increased by 0.2-0.9 units, respectively. In terms of soil enzyme activities, the treatments with rapeseed-cake and decomposing agent significantly enhanced urease (2.9%-17.0%), sucrase (3.5%-56.5%), and nitrate reductase activities (0-50.0%), whereas catalase activity decreased by 2.4%-50.0%. Microbial community analysis revealed that the treatments with rapeseed-cake and decomposing agent significantly increased soil bacterial diversity, with the relative abundance of Proteobacteria increasing by 6.1%-37.8% and its subordinate genus Sphingomonas increasing by 4.8%-90.7%, while the relative abundance of Acidobacteriota decreased by 18.9%-50.9%, respectively. Redundancy analysis showed that soil TN and SOM contents were the core environmental factors affecting the abundance of bacterial communities. These treatments effectively promoted the yield and output value of tobacco leaves, improved the coordination of chemical components of B₂F grade tobacco leaves. In conclusion, under the rape straw returning to the field, the application of decomposing agent or rapeseed-cake+decomposing agent can improve the yield and quality of tobacco leaves, and the overall effect of 450 kg/hm² rapeseed-cake + 45 kg/hm² decomposing agent was better, which is suitable for rape-tobacco closed-loop cultivation in Luoping County tobacco-planting.