The invention relates to a non-phosphorus corrosion and scale inhibitor applicable to negative hard water quality. The non-phosphorus corrosion and scale inhibitor comprises the following components in percentage by mass: 5-15% of polyepoxysuccinic acid, 5-15% of a dirt dispersion agent, 5-10% of a zinc salt, 10-40% of organotin-carboxylate, 0.1-0.5% of imidazole and the balance of water, wherein the polyepoxysuccinic acid is a liquid reagent sold in the market, the solid content of polyepoxysuccinic acid is 40%, and the polymerization degree n of polyepoxysuccinic acid is an integer within 10-50; the dirt dispersion agent is a crylic acid copolymer with AMPS; the zinc salt is zinc chloride or zinc sulfate; the organotin-carboxylate is a sodium salt of polyacrylic acid, benzoic acid or a copolymer with sulfonic acid groups, or carboxymethylcellulose; the imidazole is benzotriazole or mercapto benzoxazole. The invention further discloses a preparation method of the non-phosphorus corrosion and scale inhibitor. The method comprises the following steps: stirring and mixing the components, and filtering, thereby preparing the non-phosphorus corrosion and scale inhibitor. When adopted for negative hard water quality, the non-phosphorus corrosion and scale inhibitor disclosed by the invention is good in corrosion inhibition effect, and has the advantages of synthetic scale inhibition effect, low use amount, good stability, environmental friendliness, and the like.