The invention discloses a magnetic acrylic-acid polyamine resin capable of removing heavy metal ions and a preparation method thereof. The resin has a basic structure as described in the specification, wherein the interior of the skeleton of the resin contains magnetic particles, and R is a polyamine group. The preparation method for the resin comprises the following steps: mixing an acrylic-acid substance used as a monomer with a cross-linking agent and a pore-forming agent so as to form an oil phase, then uniformly mixing the oil phase with the magnetic particles, and carrying out suspension polymerization; and subjecting a polymerized polymer resin skeleton and polyamine molecules to ammonolysis reaction so as to obtain a final product, i.e., the magnetic acrylic-acid polyamine resin. The functionalized composite magnetic polyamine resin provided by the invention is capable of effectively and selectively removing alkaline-earth metals and the heavy metal ions, can be applied in the fields of metal enrichment, wastewater treatment, etc., and has important application prospects.