The invention relates to a preparation method of porous silicon dioxide containing a pore canal protective agent, which mainly solves the problems of greatly reduced carrier pore volume caused by a silica sol colloidal particle penetrating into a silicon dioxide pore canal in the process of preparing a silicon dioxide carrier by taking porous silicon dioxide powder as a raw material and a silica sol-containing liquid as a bonder through a forming method and lower selectivity of a vinyl acetate catalyst prepared by the silicon dioxide carrier in the traditional technique. The preparation method comprises the following steps of: (1) dipping the porous silicon dioxide into a mixture of an organic matter and a phosphorus flame retardant to obtain a precursor I; and (2) calcining the precursorI in an oxygenous atmosphere to obtain the porous silicon dioxide containing the pore canal protective agent. The technical scheme better solves the problems and can be used in industrial production for preparing a fixed bed catalyst carrier.