In order to determine reaction conditions for degree of graft(DG) of soy protein isolate - maltodextrin (SPI-MD) polymerization,optimized technology for SPI-MD degree of graft was studied using the central composite rotatable design with four variables including reaction temperature,reaction time,SPI concentration and MD/SPI ratio. Response surface methodology was used to optimize graft reaction factors in order to get the different degrees of graft of the SPI-MD grafting copolymer.The results indicated that the effect order of four factors on the yield of degree of graft was as follows:reaction temperature,SPI concentration,MD/SPI ratio and reaction time.The performance conditions for 10%,20%,30%,40%degrees of graft was also performed.