In the present article, a macromolecular polymer poly(acrylamide-allylthiourea) (PAM-ATU) was synthesized by solvent method with an average molecular weight of 1.66 x 10(4) g/mol measured by GPC. Its structure was characterized by FT-IR, H-1 NMR and C-13 NMR. PAM-ATU was used as a selective galena depressant in the flotation separation from chalcopyrite. Its flotation depressing behavior and adsorption mechanism to galena were investigated by micro-flotation, FT-IR, zeta potential, adsorption tests and X-ray Photoelectron Spectroscopy (XPS). The micro-flotation experimental results for artificially mixed minerals demonstrated that PAM-ATU was an effective depressant for galena in the separation from chalcopyrite, depressing 90.91% galena with a grade of 79.93% at pH 8.0-9.0 with 1.0 mg/L dosage. Adsorption tests showed that PAM-ATU could strongly prevent IPETC collector adsorbing onto the galena surface. However, there was no obvious influence on chalcopyrite at pH 8.0-9.0. The FT-IR spectra, zeta potential and XPS analysis demonstrated that PAM-ATU might mainly chemisorb on galena surface by S-Pb bonds. Based on this research, the adsorption model of PAM-ATU onto galena surface was proposed.