A compound heavy metal chelating agent, which relates to the field of chemical and environmental protection technology, includes dithiocarboxylate functionalized ethoxylated pentaerythritol core hyperbranched polymer and alkylene diamine-N,N′-sodium bisdithiocarboxylate with a molar ratio in a range of 1:1.0 to 1:10.0. The two different structural types of components have the synergistic positive effect. While chelating heavy metals, the compound heavy metal chelating agent alternately combine with heavy metals to form insoluble chelating super-molecular deposits, which has both chelation and flocculation functions. The compound heavy metal chelating agent meets the standard for treating heavy metal wastewater, and low concentration heavy metal wastewater. It has a wide adaptability range, and does not need to add coagulant. Moreover, it is simple in preparation method, easily available for raw materials, low in cost, and easy to be industrialized.