The invention relates to a preparation method of an activated 
vitamin D3 
drug CD ring intermediate. The preparation method comprises the following steps: carrying out 
iodine substitution on a 
diol derivative 2 to obtain a compound 3, carrying out hydroxyl reaction on the compound 3 to obtain a compound 4, carrying out Michael 
addition reaction on the compound 4 to obtain a compound 5, carrying out 
nucleophilic addition reaction on the compound 5 to obtain a compound 6, carrying out deprotection reaction on the compound 6 to obtain a compound 7, and carrying out oxidation reaction on the compound 7 to obtain a compound 1, namely, the activated 
vitamin D3 
drug CD ring intermediate (25-hydroxy Grundmann's one). The preparation method provided by the invention has the advantages that the steps are simple, the product yield is high, and massive 25-hydroxy Grundmann's one can be prepared.