The present invention relates to a method for producing a silica aerogel and a silica aerogel produced thereby. More specifically, a first water glass solution is used to form a first silica wet gel, and then a second water glass solution is additionally added to form a second silica wet gel organically bonded to the first silica wet gel which serves as a basic skeleton, so that a silica aerogel with enhanced physical properties is formed to increase the resistance to shrinkage in ambient drying, and the concentration of silicon dioxide in each of the first and second water glass solutions is controlled, thereby providing a method for producing a silica aerogel by which a silica aerogel having a specific tap density and controllable density can be produced, and also providing a silicon aerogel produced by the method.