Preparation method of agmatine

The invention discloses a preparation method of agmatine, which comprises the following steps: adjusting the pH value of fermentation liquor containing arginine decarboxylase, then sequentially carrying out activated carbon decoloration and ceramic membrane filtration to obtain filtrate, carrying out affinity chromatography on the filtrate by using a nickel column, then adding arginine slurry into the nickel column, then adding PLP (Poly Lactic Acid) in batches, and collecting liquid flowing out of the nickel column to obtain agmatine. The agmatine conversion liquid is obtained; performing membrane passing, first decoloration, electrodialysis, first concentration and first separation on the agmatine conversion liquid to obtain a agmatine crude product; re-dissolving the crude product, decolorizing for the second time, concentrating for the second time, stirring for growing crystal, and separating for the second time to obtain a gamatine refined product; and finally drying to obtain solid gamatine. The prepara