In recent years, large-scale aquaculture diseases caused by pathogenic bacteria occurs frequently, not only brought huge economic losses to fishermen, but also seriously hinder the development of aquaculture. How to fundamentally improve the aquatic environment, optimize culture model, reduce the incidence of diseases of aquatic disease, has become the common concern of aquaculture industry of all countries in the world.Antibiotics and other drugs are more effective means of disease control and prevention, but due to the abuse of antibiotics, resulting in pathogenic bacteria resistant to antibiotics and getting more serious.The development of new antibiotics is not only expensive but long development cycle. Bdellovibrio(Bdellovibrio bacteriovorus) are a class of small size, widely distributed in the sea water, sewage, soil and other habitats,move actively and Gram-negative bacteria. Bdellovibrio has the special function of" lysis"," phagocytize " pathogen which make it special bacteria of lysing pathogen, which will not lead to bacterial resistance and has no shortcomings of host specificity.So the use of Bdellovibrio in purifying water, eliminating pathogenic bacteria, applying in aquaculture will have good development prospects.Isolated,identified Bdellovibrio samples,we studied the cleavage activity of Bdellovibrio on the pathogenic bacteria in freshwater and seawater and conducted bdellovibrio cracking conditions optimization. Two samples were obtained from two areas from Dalian, both were purified by subculture and sequenced by16S rDNA, the results showed that the greatest similarity of the two samples with Bdellovibrio bacteriovonus up to100%. Two samples are both Bdellovibrio sp.208. We confirmed the Bdellovibrio activity by two methods of double plate method and liquid pyrolysis method,verified the activity of offspring obtained by subculture. Experiment show that Bdellovibrio sp.208has stable cleavage activity in seawater.Explored the optimum conditions for Bdellovibrio sp.208to lyse host E.Coli JM109:different dissolved oxygen concentration (shaking culture and static culture), in shaking culture that high concentrations of dissolved oxygen has a significant effect on Bdellovibrio sp.208cleavage of E.Coli JM109. Different culture temperature,30℃and37℃, in the whole process of lysing,temperature has no significant effect on the dissociation efficiency of Bdellovibrio sp.208. The different concentration of NaCl conditions,1.5%group cleavage ability is the best. The effect of the pH on the Bdellovibrio sp.208cleavage, when pH is7Bdellovibrio sp.208cleavage efficiency is the highest, partial acid environment is more suitable for Bdellovibrio sp.208cleavage of host. Glutamate has inhibitory effect on Bdellovibrio sp.208cleavage of E.Coli JM109; Mg2+promote lysing ability of Bdellovibrio sp.208a lot,especially3Mm; Ca2+promote lysing ability, especially7Mm. In the marine environment, Bdellovibrio sp.208is still active, still had good cleavage efficiency of E.Coli JM109.Preliminary research had been made on the Bdellovibrio lysing pathogens, separated high lysing rate, high reproductive rate and is also suitable for the marine environment.The study have a good theoretical significance of improving Bdellovibrio lysing ability and being applied in marine water quality purification.