An automatic reset air door sill comprises a bottom groove provided with an opening and a bottom wall, a left ejection-proof pressure plate is connected onto the bottom groove and to the left of the opening, a right ejection-proof pressure plate is connected onto the bottom groove and to the right of the opening, the bottom wall of the bottom groove is provided with a guide hole, a guide bar penetrates into the guide hole, the upper guide bar is movably connected with the lower bottom groove through the guide hole, a seal sill is fixedly connected to the upper end of the guide bar and comprises a seal plate, the seal plate is fixedly connected with the guide bar, the longitudinal section of the seal plate is arc-shaped, most of the seal plate is positioned above the opening, a spring is hermetically connected between the seal plate and the bottom wall of the bottom groove, a left baffle is connected to the left end of the seal plate and vertically corresponds to the left ejection-proof pressure plate, the left baffle is positioned below the left ejection-proof pressure plate, a right baffle is connected to the right end of the seal plate and vertically corresponds to the right ejection-proof pressure plate, and the right baffle is positioned below the right ejection-proof pressure plate.