The bactericidal effect of Isothiazolinones is carried out through breaking the bond between bacteria and algae protein. When contacted with microbes, Isothiazolinones can quickly inhibit their growth, thus leading to death of these microbes. Isothiazolinones has strong inhibition and biocidal effects on ordinary bacteria, fungi and alga, and has many advantages such as high biocidal efficiency, good degradation, no residual, safety in operation, good compatibleness, good stabilization, low cost in operation.