A method for preparing a silica aerogel-containing blanket, comprising: a step for preparing a reaction solution by reacting a silazane-based surface modification agent with an alcohol-based compound; a step for preparing a silica gel-base material composite by adding a silica precursor, water, and a polar organic solvent to the reaction solution to prepare a silica sol, and then immersing a base material for a blanket in the prepared silica sol to gelate the silica sol; and a step for drying the silica gel-base material composite, wherein the silazane-based surface modification agent comprises a compound of Formula 1 below, (where R 11 to R 13 and R 21 to R 23 are each independently a hydrogen atom or an alkyl group having a 1 to 8 carbon atoms, with the proviso that R 11 to R 13 and R 21 to R 23 are not simultaneously hydrogen atoms); wherein the alcohol-based compound is a linear alcohol, such as methanol, ethanol, propanol, or n-butanol, having a 1 to 4 carbon atoms, and one kind by itself, or a mixture of two or more kinds; the silica precursor is a tetraalkyl silicate, such as tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyl triethyl orthosilicate, dimethyl diethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, tetrabutyl orthosilicate, tetra secondary butyl orthosilicate, tetra tertiary butyl orthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate, or tetradodecyl orthsilicate, wherein the alkyl group may be an alkyl group having acarbon number of 1 to 20, or an cycloalkyl group having a carbon number of 3 to 20; and the base material for the blanket is polyamide, polybenzimidazole, polyaramid, an acrylic resin, a phenolic resin, polyester, polyetheretherketone (PEEK), a polyolefin (for example, polyethylene, polypropylene, or a copolymer thereof and the like), cellulose, carbon, cotton, wool, hemp fiber, a non-woven fiber, a glass fiber, or a ceramic wool. a step for preparing a reaction solution by reacting a silazane-based surface modification agent with an alcohol-based compound; a step for preparing a silica gel-base material composite by adding a silica precursor, water, and a polar organic solvent to the reaction solution to prepare a silica sol, and then immersing a base material for a blanket in the prepared silica sol to gelate the silica sol; and a step for drying the silica gel-base material composite, (where R 11 to R 13 and R 21 to R 23 are each independently a hydrogen atom or an alkyl group having a 1 to 8 carbon atoms, with the proviso that R 11 to R 13 and R 21 to R 23 are not simultaneously hydrogen atoms); wherein the alcohol-based compound is a linear alcohol, such as methanol, ethanol, propanol, or n-butanol, having a 1 to 4 carbon atoms, and one kind by itself, or a mixture of two or more kinds; the silica precursor is a tetraalkyl silicate, such as tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), methyl triethyl orthosilicate, dimethyl diethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, tetrabutyl orthosilicate, tetra secondary butyl orthosilicate, tetra tertiary butyl orthosilicate, tetrahexyl orthosilicate, tetracyclohexyl orthosilicate, or tetradodecyl orthsilicate, wherein the alkyl group may be an alkyl group having acarbon number of 1 to 20, or an cycloalkyl group having a carbon number of 3 to 20; and the base material for the blanket is polyamide, polybenzimidazole, polyaramid, an acrylic resin, a phenolic resin, polyester, polyetheretherketone (PEEK), a polyolefin (for example, polyethylene, polypropylene, or a copolymer thereof and the like), cellulose, carbon, cotton, wool, hemp fiber, a non-woven fiber, a glass fiber, or a ceramic wool.