In order to prevent and control the incidence of ulcer in large yellow croaker,we evaluated the prevalence of infection with three pathogenic vibrios in cultured Larimichthys crocea in Xiangshan by specific multiplex PCR.We collected the liver,kidney,spleen,muscle of fish in each sentinel cage randomly and detected the infection status.The results showed that there were some differences between the three kinds of pathogenic vibrios that infected the fish.The infection rate of V.alginolyticus and V.harvey large in L.crocea was higher than V.parahaemolyticus.The three vibrios were more susceptible to muscle,spleen than to the liver and kidney.The infection rate of different age of fish was not identical.In every sampling time,there existed infection rate.From July to September was the peak of infection rate and the rate increased after the typhoon certainly.In addition,according to the investigation on the relationship between incidence of ulcer and the prevalence of pathogenic vibrio,it showed that the infection rate would reach a higher value a few days before the outbreak of ulcer disease.So we could forecast the incidence and prevalence of the diseases through molecular epidemiology investigation and analyzing the infection of three pathogenic vibrios in the fish.Then,we will establish RT-PCR method of three vibrios to analyse the intensity of infection further.Thus the experimental results will be more convincing.