The invention provides a method for preparing nylon 512. Raw materials for the nylon 512 include, by weight, 27-31 parts of 1,5-pentamethylene diamine, 69-72 parts of dodecanedioic acid, 30-125 partsof distilled water, 0.002-0.02 part of molecular weight regulators and 0.005-0.015 part of antioxidants. The method includes adding aqueous solution of the 1,5-pentamethylene diamine into neutralization pots, stirring and mixing the aqueous solution of the 1,5-pentamethylene diamine with aqueous solution of the dodecanedioic acid and carrying out neutralization reaction to obtain nylon 512 salt solution; carrying out polymerization reaction on filter liquor of the nylon 512 salt solution, the molecular weight regulators and the antioxidants in polymerization kettles to obtain the finished nylon 512. The method has the advantages that as shown by detection, diversified properties of the nylon 512 prepared by the aid of the method are basically equivalent to corresponding properties of nylon612, and accordingly the nylon 512 basically can be used in individual application fields instead of the nylon 612, but is low in cost.