Provided is a method for producing a silica aerogel blanket, the method comprising recovering and reusing a supercritical waste liquid generated after a supercritical drying process. Without putting in additional equipment investments or energy, supercritical waste liquid recovered after a supercritical drying process can be reused by lowering the content of ammonium ions (NH4+) present therein through a simple adjustment of the conditions for the supercritical drying process. Thus, it is possible to produce a silica aerogel blanket while reducing the production costs thereof and preventing the deterioration of thermal insulation performance of the silica aerogel blanket.