The invention belongs to the fields of 
chemical industry and 
water treatment, and in particular relates to a compound 
bacteria and 
algae inhibitor and its application.  The composite 
bacteria and 
algae inhibitor of the present invention contains 
isothiazolinone, 2,2-dibromo-3-nitrilopropionamide, 
solvent and water, and the 
mass percentages of each component are respectively 1% to 40% of 
isothiazolinone,  2,2-dibromo-3-nitrilopropionamide 5%-40%, 
solvent 20%-60%, water 10-70%.  The compound 
bacteria and 
algae inhibitor of the present invention is a non-oxidative 
biocide. When the bacteria and algae inhibitor is applied to a 
water treatment system, the 
impact type 
intermittent dosing method is adopted, and the dosage of the bacteria and algae inhibitor per 
liter of water is 1 mg to 100 mg.  .  The components of the formula of the present invention have obvious synergistic effect, good compatibility with scale inhibitors and 
corrosion inhibitors, low biological 
toxicity, high biodegradable rate, and have killing and inhibiting effects on 
planktonic bacteria and algae in water,  It has stripping and inhibiting effects on the bacteria and algae adherents that grow on the surface of the equipment.  In practical application, it has the advantages of small addition amount, low use cost, convenient operation and no 
pollution.