Dialdehyde starch was extensively used abroad but it is scarcely produced and applied in China. The technology for producing dialdehyde starch was systematically studied in this experiment. The optimal conditions for producing dialdehyde starch was obtained. The experimental results show that dialdehyde starch can be prepared at 35～40℃ for 3 h with other conditions of sodium periodate-starch mole ratio of 1.1, sodium periodate concentration of 0.7 M and pH value of 1.2～1.5 and the dialdehyde content of final product is more than 95%.