Five kinds of bacteria were isolated from disease Meretrix meretrix and culture water (two isolated from the M. meretrix, three from the culture water) in Lvsi harbor, Jiangsu province. The results of infection showed that strain WG1702 can cause disease with the mortality rate 100 percent and the same symptoms as original. It was cued that strain WG1702 was the pathogenic bacteria and caused the death in large scare, a preliminary research was done on the bacteria including morphological, physiological, biochemical characteristics, phylogenetic position and pathogenic. Strain WG1702 was a straight-rod gram negative bacterium, the physiological and biochemical indicators were lysine decarboxylase, ornithine decarboxylase, reduction of NO3- to NO2-, mannitose, oxidase and methylred reaction positive, arginine decarboxylase, arginine dihydrolase, salicin and voges-proskauer negative. In order to identify the bacteria phylogenetic position and a 16S rRNA molecular identification was done, PCR amplification got a size of about 1.5 kb gene fragment, The whole 16S rRNA sequences were determined, analyzed the homology of sequences and built the phylogenetic tree. Sequences analysis revealed that strain WG1702 exhibited the highest level of 97.4% similarity to Vibrio harveyi(DQ146937), combining morphological, physiological and biochemical identification results, the isolated strain WG1702 was identified as Vibrio harveyi.