Abstract: The thermoplastic copolymers(T-SPI) were prepared from soy protein isolate(SPI) grafted with methyl acrylate(MA) and methyl methacrylate(MMA) in urea aqueous solution with ammonium persulfate as initiator and sodium sulfite as denaturant. The influences of the reaction conditions on the grafting rate were investigated. The grafting rate of 16g SPI was preferable under the conditions of urea concentration 2mol/L, initiator concentration 35mmol/L, monomer concentration 1.23mol/L, reaction temperature 70℃, reaction time 4h in 250mL deionized water. The material was analyzed by means of FT-IR, DSC and torque rheometer. The results indicated: the monomer is grafted on SPI successfully, and T-SPI has a glass transition temperature of 66.35℃, the plasticizing time is 113s. All of them proved that this material has a good thermoplasticity.