Abstract: Dextran(DEX)and soy protein isolate(SPI)were used as materials to study the preparation technology of SPI-DEX conjugates in order to research conjugation technique with the mild condition,high grafting degree and low browning degree. The material ratio,grafting temperature and grafting time were selected as factors to carry out the single factor experiment. The response surface method was applied to optimize technical parameters of preparation using material ratio,grafting temperature,grafting time as variables,and degree of grafting as response value. The physicochemical properties were analyzed on SPI-DEX conjugates. The results showed that the optimum parameters were the material ratio 1:1.2,grafting temperature 83 ℃ and grafting time 7.3 h. Under this condition,the optimum parameters reached to 56.38% and the browning degree was 0.041.Moreover,properties of SPI-DEX conjugates were also studied by SDS-PAGE and amino acids analysis. The results exhibited dextran grafted on the protein exactly. The solubility of the SPI-DEX at pH=7.0 increased by 40.48% in comparison with SPI. The emulsifying activity and emulsifying stability increased by 69.76% and 62.11% compared with SPI.