The invention discloses a method for preparing double metal cyanide catalyst, so as to obtain the double metal cyanide catalyst with the structure of Aa Bb Cc Dd (H2O) e. The method comprises: halide water solution which has a certain concentration and contains one or more divalent metal(s) is gradually dripped with cyanide water solution containing one or more variable valency metal(s) B; after being filtered and fully washed for reaction, precipitate can be formed; then, chelating agent is added for reaction; after being separated and dried, the double metal cyanide catalyst can be obtained. The preparation method is simple and does not produce a great deal of waste water which is harmful to the environment; the unreacted chelating agent can be recycled, so that the production cost is low, and the method is beneficial to environmental protection. When being applied to the copolymerization of carbon dioxide/epoxide, the catalyst has good application effect.