Disclosed is a seat overturning mechanism, comprising a support, a cover plate, two connecting plates, a cushion skeleton and two springs. The support whose one side edge is fixedly connected with a seat is arranged on the floor. The cover plate which is perpendicular to the floor is arranged on the external side of the support. The two ends of every connecting plate are respectively rotatablely connected with the support and the cover plate. The cushion skeleton which is arranged on the horizontal position above the support and the cover plate is respectively rotatablely connected with the support and the cover plate, and in addition, the cushion skeleton overturns around a join point to a position perpendicular to the floor. The two ends of every spring are respectively connected with the cushion skeleton and the support. When the cushion skeleton is positioned in the horizontal position and in the vertical position, the two springs generate the strength to prevent the cushion overturning. The overturning mechanism with the structure is of safety, is of firmness, is of good reliability, is of little space occupation and is of wide use in business cars and small-sized buses.