The present invention provides a method for preparing a blanket containing a silica aerogel, and a blanket prepared by using the same and containing a silica aerogel, the method comprising the steps of: preparing a sol by mixing a water glass solution, a polar organic solvent and a silazane-based surface modifier; preparing a silica gel-substrate composite by dipping a substrate for a blanket into the sol and gellifying the same; and drying the silica gel-substrate composite. A blanket containing a silica aerogel and having high hydrophobicity and excellent physical properties, particularly, low tap density, high porosity and excellent mechanical flexibility can be prepared by using the least amount of a surface modifier without an additional surface modification step through the preparation method.