In this study, cellulose-degrading strains with plant growth promotion were isolated and screened from wheat and corn rotation system in Shajiang black soil to achieve resource utilization of straw and high-stable maize production. By monitoring carboxymethyl cellulase activity (CMC) and indoleacetic acid (IAA) secretion, a high IAA-production ability strain with excellent efficiency in cellulose breakdown was identified. The X2 strain was identified as Rhizobium pusense based on morphology and physiological and biochemical properties as well as 16S rRNA gene sequence analysis. It was found that the straw degradation ratio could reach to 16.1% on the 15 d of liquid fermentation conditions, which was 65.4% higher than that of the control; in addition, alkaline nitrogen content in the potted soil was significantly higher than that of the control after inoculation with this strain. The average root diameter, surface area, and above-ground dry weight of the plants increased significantly by 22.0%, 28.6%, and 33.3%, respectively. To further improve the activity of the strain, the culture conditions of the strain were optimized using a single-factor test. The maximum growth, CMC activity, and IAA production were obtained at optimal fermentation conditions (liquid volume 25 mL/250 mL, yeast powderas nitrogen source, and pH 5.0-6.0). In summary, the sieved X2 strain has the ability of straw degradation and maize promotion, it can provide a new microbial resource for straw resource utilization in Shajiang black soil area.