The application discloses an imidazoline biguanide sulfate bactericide for water treatment and a preparation method of the bactericide. The preparation method comprises the following steps: according to parts by weight, weighing the following materials: thiourea dioxide, dodecyl trimethyl ammonium bromide, hydrogen peroxide, brominated 1-butyl-2,3-dimethylimidazole, water, dodecylguanidine acetate, a polymerization inhibitor, sodium metasilicate pentahydrate, sulfuric acid, hexadecyl dimethyl benzyl ammonium chloride, a dispersing agent, dioctadecyl dimethyl ammonium chloride, imidazoline, triethylene tetramine and ethanol, and uniformly mixing the weighed materials; the scale inhibiting ratio of the product is 70-90%, and sterilizing rate on escherichia coli, staphylococcus aureus, candida albicans, gonococcus, penicillium, aspergillus, saprophytic bacteria and salmonella is 97.9-99.9%; when the bactericide is kept at 50-60 DEG C for one month, the sterilizing rate is 97.5-99.5%, when the bactericide is kept at 40-50 DEG C for half an year, the sterilizing rate is 97-99%, and when the bactericide is kept at room temperature for 1-2 years, the sterilizing rate is 94-98%.