The hydrophilic channels for water permeation with the selective rejection ability towards heavy metal ions were constructed in a novel forward osmosis (FO) membrane using polyethyleneimine (PEI) and zein, which improved the separation efficiency of the prepared FO membrane and exhibited the expected performance in the treatment of heavy metal ion wastewaters. The PEI/zein active layer was prepared by one-step method at the gas-liquid interface based on the non-solvent induced phase separation process. PEI as a functional medium imparted the significantly improved hydrophilicity, adsorption ability and water permeability on the zein layer. The rejection ability of heavy metal ions by the PEI/zein active layer was significantly improved based on the strong complexation ability of PEI, and the rejection ratios of Cd(II), Ni(II), Pb(II) and Cu(II) ions were more than 97%. In addition, with the preferential occupancy of Cu(II) ions in the water channel of the prepared FO membrane, the rejection ratios of Cd(II), Ni(II) and Pb(II) ions were further improved to be more than 99.5%. The excellent membrane-forming ability and machinability of zein provide a basis for the FO performance improvement via the introduction of functionalities. This paper aims to provide new ideas for the preparation of efficient FO membranes and extend the application scope of the current FO technology.