Abstract: Enhancing cellulase activity and stability is essential for addressing energy and environmental challenges. We isolated a halophilic strain, Y3, with cellulase activity from a water sample from Yuncheng Salt Lake. Preliminary identification was conducted through Gram staining, 16S rRNA gene sequencing, and phylogenetic analysis, classifying Y3 as Bacillus stercoris. Optimal culture conditions for Y3 were determined as 15.0% NaCl, 45.0 ℃, and pH 8.0, while the optimal reaction conditions for its cellulase were 20.0% NaCl, 45.0 ℃, and pH 9.0, with minimal impact on activity from chloroform. After UV mutagenesis, the resulting strain Y3M showed significantly enhanced cellulase activity, reaching (102.4±3.7) U/mL under conditions of 20.0% NaCl, 50.0 ℃, and pH 9.0, a 2.14-fold increase compared to the original strain. The UV-induced mutations improved both the activity and stability of Y3 cellulase, making the mutated strain and its cellulase more promising for applications in variable environments.