The invention discloses a heavy metal chelating agent. The heavy metal chelating agent is formed by copolymerizing dithiocarbamate and cationic monomers. The heavy metal chelating agent has the beneficial effects that the heavy metal chelating agent has strong heavy metal ion chelating effects and good stability, can be used for industrial wastewater which has pH value of 2-13 and contains heavy metal ions and complex ions and effectively generates water-insoluble sulfide precipitates with the heavy metal ions and the complex ions; hydrogen sulfide is not generated under the strongly acidic condition; the treated industrial wastewater conforms to the state-specified emission standard; heavy metals can be recovered from the precipitates generated after treatment, thus not causing secondary pollution. Meanwhile, the invention also discloses a preparation method of the heavy metal chelating agent.