The invention discloses a preparation method of a lignin-based dithiocarbamate heavy metal ion capture agent. The method comprises the steps of: (1) adding water into lignin and stirring them, adding an alkaline conditioning agent to adjust the pH to 9-11, then adding an oxidizing agent, conducting heating to raise the temperature to 80-90DEG C for reacting for 1-2 hours; (2) adding an amination reagent, maintaining the reaction temperature at 80-90DEG C, then adding formaldehyde to react for 5-6 hours; (3) cooling the solution to room temperature, adjusting the pH value to 10-11, then adding carbon disulfide to perform an esterification reaction for 4-5 hours at 40-45DEG C; and (4) adding a modifier for reacting for 1-2 hours, then carrying out pumping filtration, and then conducting washing 2-3 times with water and absolute ethyl alcohol, thus obtaining a solid product, i.e. the lignin-based dithiocarbamate. The lignin-based dithiocarbamate heavy metal ion capture agent provided in the invention has the advantages of simple preparation process, low production cost, excellent performance, adaptability to treatment of various heavy metal ion polluted wastewater, good stability, and wide applicable range.