Salmonid alphavirus（SAV）is the pathogen of salmon pancreas disease（PD），mainly infects fishes in salmonidae family. At present，SAV hasn't been isolated in China yet. In order to improve the detection efficiency of SAV，3 pairs of specific primers were designed according to the nsP1 gene segment，and a reverse transcription mediated isothermal amplification（RT-LAMP）method for detecting SAV was established. The reaction system was 25 μL，the optimized reaction temperature was 65 ℃，and the reaction time was 1 h. The minimum detection limit was 10 copies of viral nucleic acids. Specificity tests showed that，the developed method didn't have any cross-reactions with other RNA viruses，including infectious salmon anaemia virus，viral haemorrhagic septicaemia virus，infectious haematopoietic necrosis virus，viral nervous necrosis，grass carp reovirus，and spring viraemia of carp virus. After the addition of dyes，the reaction results was directly visible to the naked eyes. In summary，a specific，convenient detection method was developed，and it was suitable for SAV primary screening and nucleic acid detection.