The invention belongs to the field of hypersonic speed wind tunnels, and relates to an air inflation axial sealing device used in a vacuum environment. The air inflation axial sealing device comprises an air inflation sealing ring, a sealed barrel, a through connection sleeve, an air inflation pipeline and an air compressor. The air inflation sealing ring, the sealed barrel and the through connection sleeve are of axisymmetric structures. The air inflation sealing ring is mounted in a groove of the through connection sleeve, and an air inflation connector of the air inflation sealing ring is matched with an air inflation connector of the through connection sleeve. The sealed barrel enters the through connection sleeve, and therefore the sealing ring can be in full contact with the outer surface of the sealed barrel after being inflated. The air inflation pipeline is connected with the air compressor and an inflation opening of the air inflation sealing ring. According to the air inflation axial sealing device, the defect of a corrugated pipe joint manner is overcome, investment and running cost is reduced, the labor intensity and the pipeline equipment replacement difficulty are reduced, and the pipeline equipment replacement frequency is improved; and a good vibration isolation effect is achieved, and the air inflation axial sealing device can be applied to axial vacuum sealing between pipeline equipment with different apertures.