A method of folding a knee airbag includes folding a lower portion of the knee airbag perpendicularly to a vertical central axis so that a lower end of the knee airbag is placed on the front panel of the knee airbag, individually folding both sides of the knee airbag toward the vertical central axis, and rolling an upper end portion of the knee airbag toward the lower portion of the knee airbag. The lower portion of the folded knee airbag is rapidly deployed toward the leg of an occupant in the initial deployment of the knee airbag, thereby minimizing time to ensure the minimum space between the instrument panel and the leg of the occupant and rapidly confining the leg of the occupant.