Efficient composite germicide for circulating water system and preparation method thereof

The invention discloses an efficient composite germicide for a circulating water system, which is composed of the following components: 15-18% of glutaraldehyde, 42-49% of quaternary phosphonium, 11-17% of isothiazolinone, 20-30% of deionized water, and 5-8% of dithiocyano-methane. The germicide has an extremely excellent bactericidal effect, can be used in circulating cooling water under high pH value conditions, has a good killing effect on heterotrophic bacteria, sulfate reducing bacteria and algae, and especially has an obvious killing effect on heterotrophic bacteria; and the germicide is high in killing speed, strong in killing force, and low in toxicity.