The invention relates to a method for preparing cadaverine comprising: (1) obtaining an aqueous cadaverine salt composition from a fermentation system; (2) adjusting the pH of the aqueous cadaverine salt composition to a pH of at least about 12 by adding an inorganic base composition to provide a first composition comprising an aqueous cadaverine composition having a pH of at least about 12 and a solid composition comprising one or more alkali metal sulfates; (3) subjecting the first composition to solid-liquid separation without organic solvent extraction to provide the aqueous cadaverine composition and the solid composition; (4) distilling or evaporating the aqueous cadaverine composition of step (3) without organic solvent extraction to provide purified cadaverine; (5) preparing a saturated solution of the alkali metal sulfate(s) from the solid composition of step (3) at a temperature of about 35-40° C., mixing the saturated solution with NH4HCO3, and subjecting the mixture to solid-liquid separation to provide Solution (I) and Solid (I); (6) adjusting the temperature of Solution (I) to about 60-80° C., and obtaining Solution (II) and Solid (II) after solid-liquid separation; (7) concentrating Solution (II) and obtaining Solution (III) and Solid (III) after solid-liquid separation; and (8) adding Solid (III) back to the fermentation system of step (1); wherein steps (1) to (8) are optionally repeated one or more times.