A method for folding a knee airbag may include: folding both sides of an airbag cushion a plurality of times, and fixing the folded portion of the airbag cushion; forming a roll folding part by rolling one side of the airbag cushion of which both sides are folded a plurality of times; and folding the other side of the airbag cushion toward the roll folding part, with the roll folding part formed at the one side of the airbag cushion, and fixing the other side of the airbag cushion.