The invention relates to a preparation method of a non-phosphorus corrosion and scale inhibitor. The preparation method of the non-phosphorus corrosion and scale inhibitor is characterized by being blended from the following components in percentage by weight: 1) 5-15% of polyepoxysuccinic acid, 2) 5-15% of a dirt dispersion agent, 3) 20-50% of organic carboxylic acid, 4) 5-10% of zinc salt, 5) 0.1-0.5% of imidazole, 6) 0.5-3% of an inorganic corrosion inhibitor, and 7) the balance of water according to mass percent, wherein the polyepoxysuccinic acid is a market-sold liquid preparation, the solid content is 40%, and the degree of polymerization n is an integer of 10-50. The preparation steps are as follows: adding the zinc salt and the inorganic corrosion inhibitor in a fixed amount of water, fully stirring to completely dissolve the zinc salt and the inorganic corrosion inhibitor, then adding the polyepoxysuccinic acid, the dirt dispersion agent and the organic carboxylic acid, fully stirring, finally adding the imidazole until the imidazole is completely dissolved, and filtering.