Disclosed herein is a method of preparing a silica aerogel. The silica aerogel is prepared by adding a first water glass solution and an acid catalyst to a reactor to form a first silica wet gel. The method further includes adding a second water glass solution and an acid catalyst to the first silica wet gel. The method further includes adding a surface modifier solution to the first silica wet gel to form a second silica wet gel. The method further includes drying a silica wet gel including the first silica wet gel and the second silica wet gel. The prepared silica aerogel has a tap density of 0.032 to 0.070 g/mL and a carbon content of 11.2 to 12.1 wt %.