Provided are a preparation method of a silica aerogel-containing blanket which includes mixing a water glass solution, a polar organic solvent, and a silazane-based surface modifier to prepare a sol, preparing a silica gel-base material composite by immersion and gelation of a base material for a blanket in the sol, and drying the silica gel-base material composite, and a silica aerogel-containing blanket prepared by using the preparation method. A silica aerogel-containing blanket having a high degree of hydrophobicity as well as excellent physical properties, particularly, low tap density, high porosity, and excellent mechanical flexibility can be prepared by the minimal use of a surface modifier without a surface modification step by the above method.