Waterborne epoxy resin with carboxyl was prepared by allyl glycidyl ether (AGE) and methacrylic acid (MAA) through one-step method based on the theory of free radical copolymerization. The influences of feeding way, initiator species and initiator dosages on the properties of polymer were discussed. The structure of polymer was characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and Hydrogen Nuclear Magnetic Resonance (1H NMR), and the polymer was used in leather tanning. The results showed that the optimum synthesized conditions as follows: the initiating system was oxidoreduction system, the ammonium persulfate (APS) dosage was 11%, the monomer and APS were dropping in the polymerization process. Application results indicated that the shrinkage temperature of the leather tanned by polymer was 71℃, and the thickness increment ratio was 46%. The shrinkage temperature of the leather tanned by polymer associated with 3% chromium was 114.1℃, and thickness increment ratio resched 104%. Meanwhile, compared with the traditional chrome tanning method, the tanning process which tanned by polymer associated with 3% chromium reduced the Cr2O3 content of effluent effectively.