For rapid detecting the virus disease, largemouth bass ulcerative syndrome, which broke out in cultured largemouth bass () in Guangdong Province, ) gene of LBUSV was identified by genome walking. gene is 1 392 bp encoding 463 amino acids. Multiple alignment analysis indicated that the virus belonged to the genus of family Iridoviridae. A pair of specific primers was designed and synthesized to amplify a fragment for virus detection. Optimizing PCR reaction condition showed that the suitable annealing temperature ranged from 59, and the suitable cycle number was 30. PCR sensitivity assay indicated that the PCR method could detect Lwithin 30 PCR cycles. The method could detect naturally ISKNV-infected fish had no amplified products. In addition, the method shares many advantages, such as rapidness, lower-cost, exactness, therefore the PCR method will be applied extensively.