Abstract: ObjectiveTo study the bactericidal efficacy and influencing fators of chloride to legionella pneumophila.Methods The solution quantitative germicidal test was performed to observe the germicial efficacy of Legionella pneumophila as well as the role of temperature,pH and organic substance.ResultsThe killing rate to Legionella pneumphila was 100% when the effective chloride was 500mg/L and 1000mg/L lasted 1min.The same results was got when the effective chloride was 100mg/L lasted 10min and 250mg/L lasted 5min respectively.The bactericidal efficacy was enhanced with the growth of temperature and drop of pH.The efficacy was lowed with organic substance.ConclusionThe results revealed that chloride could be used for the bactericide of legionella penumophila in environment water and air.