The invention discloses a synthesis method of a beta-cyclodextrin derivative. The synthesis method comprises the following steps: in DMF, in the presence of Et3N, CuI and ascorbic acid, carrying a linkage reaction among 6A,6D-dideoxydiazidocyclodextrin and 1-O-(2-propargyl)-beta-D-lactoside, then carrying out a reaction with 1-O-2-propargyl-beta-D-galactoside to obtain a mixed galactosyl and lactosyl modified beta-cyclodextrin derivative. The synthesis method is simple and easy to operate; by the synthesis method, the yield is high; when the beta-cyclodextrin derivative is used as a medicine carrier, the targeting ability, the solubility and the stability of a liver cancer medicine can be improved. The invention further provides a synthesis method of the 6A,6D-dideoxydiazidocyclodextrin, by which the defects that in the prior art, the synthesis method of the 6A,6D-dideoxydiazidocyclodextrin is complex, the yield is low and spectral characterization is not satisfactory are overcome.