The invention discloses an overturning locking mechanism for an integrally-turnable passenger seat of large-sized and medium-sized buses. The overturning locking mechanism comprises rotating shafts, locking mechanisms and pulling handles, wherein each rotating shaft is arranged on a support seat, and seat bodies are rotatably connected with the rotating shafts; lock tongues of each locking mechanism are fixed on the corresponding seat body, lock pins are fixed on each support seat, and the lock pins and the corresponding lock tongues cooperate lock up the seat; the lock tongues can be driven to rotate through transmission mechanisms connected with the lock tongues, so that the lock tongues can be separated from the corresponding lock pins for unlocking, and further, overturning is realized. According to the invention, the integrally-turnable passenger seat can be integrally turned directly by virtue of the connection between the rotating shafts and the support seats, so that the operation is convenient; through the arrangement of the locking mechanisms, the seat bodies and the corresponding support seats can be locked up when the seat is not required to be turned, so that the stability of the seat is guaranteed; when the seat is required to be turned, the handles are pulled to separate the lock tongues and the lock pins, and the seat bodies can be directly turned, so that the operation is simple, and misoperation and potential safety hazard are avoided.