The leather retanning agents of SA type have have been preparated by emulsion copolymeriation between acrylic monomers and unsaturated sulfated castor oil. The properties and structure of copolymers have been studied by IR, NMR, DSC, WAXD methods and so on. Accordlng to the features of spectrum, we provided an approximate mechanism by which the graft copolymerization occurs between the sulfated oil and the main chain of acrylic copolymers.