[Objectives] The purpose of this study was to isolate strains capable of efficiently decomposing cellulose from the intestines of Muskrat (Ondatra zibethicus), so as to provide strain resources for the development of microbial preparations of cellulose decomposing bacteria. [Methods] Six cellulose decomposing bacteria were isolated from the cecum of Muskrat using the culture medium with sodium carboxymethyl cellulose (CMC-Na) as the only carbon source. The Congo red staining experiment and the determination of carboxymethyl cellulase (CMCase) activity were carried out. Bacterium strain WJ-3 with highly efficient cellulose decomposing activity was screened, and further identified by morphological observation, physiological and biochemical analysis as well as 16S rDNA gene sequencing approach. The 16S rDNA gene sequence was analyzed by BLAST in national center for biotechnology information (NCBI), and the phylogenetic tree was constructed by MEGA 6.0 software. The enzymatic characteristics of CMCase produced were tested to analyze the optimal reaction pH and temperature of the cellulase, as well as the tolerance of the cellulase to different temperatures and pH values. Ultimately, all the data were processed with Spss 23.0 software. [Results] A strain WJ-3 with efficient cellulose decomposing activity was identified and it was agram-positive, spore-forming, and rod-shaped bacterium (Fig. 2, Fig. 3). The physiological and biochemical test results of strain WJ-3 were shown in Table 2. By the 16S rDNA gene sequence analysis, strain WJ-3 was identified as Bacillus aerius, and named Bacillus aerius WJ-3 (GenBank Accession: MZ 292092.1). The phylogenetic tree of strain WJ-3 was shown in Figure. 5. When the CMCase produced by strain WJ-3 reacted in the range of pH 4.0﹣6.0, the enzyme activity increased with the increase of pH value, and the best reaction pH was 6.0 (Fig. 6), and the cellulase could maintain more than 80% of the relative enzyme activity after being stored in the range of pH 4.0﹣8.0 for 30 min (Fig. 7); When the CMCase produced by strain WJ-3 reacted in the temperature range of 30﹣50 ℃, the enzyme activity gradually increased with the increase of temperature, the enzyme activity was the highest at 50 ℃ (Fig. 8), and then the enzyme activity of CMCase decreased with the increase of temperature, the cellulase could maintain high enzyme activity after being stored in the temperature range of 30﹣50 ℃ for 30 min (Fig. 9). [Conclusion] The enzyme activity of CMCase produced by strain Bacillus aerius WJ-3 is relatively high, with satisfactory acid and alkali resistance as well as thermal stability. It is a strain resource with certain utilization value.