The invention provides a method for preparing 1,5-pentanediamine. The method comprises the steps of: a, dissolving lysine salt to obtain an aqueous solution of lysine salt; b, adding lysine decarboxylase and vitamin B6 coenzyme to the aqueous solution of lysine salt for a decarboxylation reaction of lysine; c. filtering a 1,5-pentanediamine salt solution obtained in step b by using an ultrafiltration membrane having a interception molecular weight being 3000-6000; d. selectively adsorbing vitamin B6 coenzyme in a 1,5-pentanediamine salt ultrafiltrate obtained in step c by using macroporous adsorption resin; e, sending the enzyme-removed 1,5-pentanediamine salt solution obtained in step d to a two-chamber bipolar membrane electrodialysis device for desalting; and f. performing concentrationand dehydration on the 1,5-pentanediamine aqueous solution obtained in the step e, then performing vacuum distillation, and performing condensation on a light phase to obtain a 1,5-pentanediamine product. The preparation method of the invention has the advantages of low cost, small environmental protection pressure, and high product purity, and is suitable for industrial application.