NOVELTY - Preparing dimethoxy docetaxel (I), comprises: (1) performing condensation of a tetracyclic compound (II) with trichloroethyl chloroformate in a reaction solvent to obtain tetracyclic ester compound (III); (2) performing the condensation of (III) with phenyl-cyclobutanone compound (IV) and sodium bis(trimethylsilyl) amide in an ether solvent to obtain tetracyclic chloro ester compound (V); (3) acidifying (V) in alcohol solution of zinc, and performing etherification with an etherifying agent in an ether solvent under the catalysis of inorganic alkali, adding acid for hydrolysis to obtain (I).    USE - (I) is useful for treating prostate cancer patient.    ADVANTAGE - The process: has less reaction steps, shortens reaction period and provides (I) with high purity and high yield. The process is simple and ecofriendly, and can be carried out using inexpensive raw material and suitable for industrial production.    DETAILED DESCRIPTION - Preparing dimethoxy docetaxel of formula (I), comprises: (1) performing condensation of a tetracyclic compound of formula (II) with trichloroethyl chloroformate in a reaction solvent to obtain tetracyclic ester compound of formula (III), where the reaction solvent comprises one or more of anhydrous pyridine, triethylamine, N-methylmorpholine or N,N-diisopropylethylamine; (2) performing the condensation of (III) with phenyl-cyclobutanone compound of formula (IV) and sodium bis(trimethylsilyl) amide in an ether solvent to obtain tetracyclic chloro ester compound of formula (V), where the ether solvent comprises dimethylsulfoxide (DMSO), dimethyl formamide (DMF), dimethylacetamide (DMA) or anhydrous tetrahydrofuran; (3) acidifying (V) in alcohol solution of zinc, and performing etherification with an etherifying agent in an ether solvent under the catalysis of inorganic alkali, adding acid for hydrolysis to obtain (I), where the: ether solvent comprises DMSO, DMF, DMA or anhydrous tetrahydrofuran; etherifying agent comprises one or more dimethyl sulfate, methyl iodide or dimethyl carbonate; inorganic alkali comprises sodium hydride, n-butyl lithium or potassium hydride; and acid comprises glacial acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid.