The invention provides an air cushion used for lifting buttocks of a pregnant woman for treatment during premature rupture of the membrane of the pregnant woman. The air cushion comprises an upper part and a lower part, wherein the upper part is a longitudinal rectangle from an overlook view and is a triangle from top down from a lateral view, and an air inflation hole, an air inflation tube, an air inflation piston and an air inflation ball are arranged on a side surface; and the lower part is a transverse rectangle from the overlook view and is a rectangle slightly higher than the bottom edge of the triangle from the lateral view, and an air inflation hole, an air inflation tube, an air inflation piston and an air inflation ball are arranged on a side surface. The air cushion solves the problems that at present, when premature rupture of the membrane occurs on the pregnant woman, the amniotic fluid flows out, the buttocks are in urgent need of being lifted for treatment, while the traditional method which adopts toilet paper to support below the buttocks is unreliable in effect, inconvenient to use, unsafe and uncomfortable. The air cushion which is lifted gradually from top down can relieve the discomfort in the waist part, the back part and the shoulder part caused by lifting of the buttocks, can be folded, packaged and placed in a carried bag in a non-inflation state for emergency, and is portable. During premature rupture of the membrane of the pregnant woman, the pregnant woman lies the buttocks lifting air cushion, so that complications such as oligohydramnios, prolapse of umbilical cord, fetal distress, and even intrauterine death and the like caused by outflow of the amniotic fluid can be prevented or reduced, and the buttocks lifting operation for treatment is simple, convenient and safe.