According to the invention, an Alivibrio salmonicida strain is separated from Paralichthys olivaceus cultured in China. The strain has strong pathogenicity to Paralichthys olivaceus and Atlantic salmon and is preserved under the accession number of CCTCC M 2018086. In experiments, an inactivated vaccine prepared from the strain can realize an immune protective rate of 80% or more, and the durationof the immunoprotection lasts for 6 months or more; so it is indicated that the vaccine prepared from Alivibrio salmonicida PO-1 has the immunoprotective effect on Alivibrio salmonicida. The Alivibrio salmonicida strain is applicable to preparation of the vaccine and has the application prospects of vaccine development.