The potential environmental pollution of chrome tanned leather results in the development of ecological chromium-free leather tanning production in leather industry. However, with weakly positive charge, chromium-free tanned leather cannot strongly bind to anionic dyes, thus causing low quality of finished leather. Herein, p(DM-co-[DDVIM]Br)PS was synthesized by free radical polymerization method. The structure and properties of the targeted products were synthetically characterized. The results indicated that the use of p(DM-co-[DDVIM]Br)PS fatliquoring agent can not only make leather fibers become loose, but also improve the binding affinity between leather and anionic dye during the fatliquoring process. The fatliquoring agent adsorption rates and the dye absorption rate of the leather were as high as 99.26% and 99.01%, respectively; the fatliquoring and dye solutions were clear, so they can be used as clean materials in the fatliquoring process of chromium-free tanned leather. Leather treated with p(DM-co-[DDVIM]Br)PS fatliquoring agent had higher K/S value (12.80) and is softer than those treated with commercial fatliquoring agent. Consequently, this study can not only help improve the absorption rate of anionic wet finishing materials, but also reduce the pollution caused by chrome tanning agents, thus providing a new way for the cleaner production in leather industry.