Abstract: A Cynoglossus semilaevis fish farm in Changli County, Hebei Province, developed a disease in mid-June 2022. In order to isolate the dominant infection bacteria from the ascites of the dead Cynoglossus semilaevis, bacterial isolation and purification, Gram staining, biochemical identification, and 16 S rRNA sequence analysis were used in the experiment. The Kirby-Bauer test paper method was used to detect the sensitivity of the isolated bacteria to 22 kinds of antibiotics, and the agar diffusion method was used to detect the bacteriostatic effect of 22 kinds of traditional Chinese medicines. The results showed that the isolated bacteria cultured in blood agar medium were smooth, round, gray and convex, β-hemolytic colony; Gram staining and microscopic examination showed negative bacilli. The coincidence rate of biochemical characteristics with that of Shewanella algae was 96%. The homology of 16 S rRNA gene sequence of the isolated bacteria with that of Shewanella algae in GenBank was 98.94%. The isolates were sensitive to ceftriaxone, ceftiofur and spectinomycin, and resistant to ampicillin, amoxicillin and kanamycin. Schisandra chinensis, Fructus chebulae and Terminalia chebula had the strongest bacteriostatic effect on the isolated bacteria, while 11 traditional Chinese medicines such as Cortex fraxini, Cortex phellodendri and Herba violae had no bacteriostatic effect. The results suggested that the isolated strain was Shewanella algae, which was sensitive to antibiotics ceftriaxone, ceftiofurol, megamycin, Chinese traditional medicine Schisandra chinensis, Fructus chebulae and Terminalia chebula.