Knee protective airbag

The invention relates to a knee protective air vesicle, which can be folded under the steering post at the front of driver, and inserted under the key hole that hanging accessory. When air flows in, it can expand to protect the knee of driver; the air vesicle comprises a covering part that fully covering the back part near the key hole and a general part; the covering part uses seams to meet the side wall of steering post and the side wall of driver to be expanded when the general part is fully expanded; the seam part is arranged near the external edge of covering part and its internal side. The invention can avoid impacting the key and protect the knee of driver.