Abstract: This study used sodium alginate as sole carbon source. Ten high-yielding alginate lyase strains were isolated from algae and seawater samples from Maowei Sea in Guangxi. After 16 S rDNA phylogenetic analysis,the strains were classified into the genus Halomonas, Pseudoalmonas and Vibrio, respectively. To further explore the evolutionary history of alginate lyase（ALG）, the study collected homologous sequences of the alg gene from GenBank. The potential positive selection site of the alg gene was confirmed by phylogenetic analysis, maximum likelihood analysis, using a site model and a branch site model. Positive selection evolution analysis results showed that 4 Y, 16 I, 40 N, 61 L, 91 T, 99 S, 149 L, and 154 S were the positive selection sites of the alg gene, which indicated that forward environmental pressures may promote the evolution of the alg gene. This study provided an important scientific basis and theoretical support for subsequent related researches such as directed mutagenesis or the structure and function modification of the alg enzyme.