The invention discloses a genetically engineered bacterium for expressing beta cyclodextrin glycosyl transferase as well as a construction method and a use thereof. The genetically engineered bacterium for expressing the beta cyclodextrin glycosyl transferase is genetically engineered bacterium E. coli BL21(DE3)/pET22-cgt obtained by transforming recombinant expression plasmid pET22-cgt which is obtained by inserting a beta cyclodextrin glycosyl transferase gene obtained by cloning into an expression vector pET22b(+) in host bacteria E.coliBL21(DE3). The genetically engineered bacterium for highly expressing beta-CGTase, constructed by the construction method disclosed by the invention, can be used for changing a culture medium of original microorganisms, separating thalli which appear in a production process of the bacteria to obtain relatively pure beta-CGTase, and directly preparing beta-CD by virtue of the beta cyclodextrin glycosyl transferase, so that the existing domestic beta-CD production process is radically improved to obtain high-quality beta-CD.