A turnover mechanism, comprising: a bracket assembly; a rotatable cam axially disposed on the bracket assembly; a cam resetting component connected to the cam and the bracket assembly; a locking pawl piece axially disposed on the bracket assembly, the cam driving the locking pawl piece to move between a locked state and an unlocked state through forward and reverse movements; a rotating shaft axially disposed on the bracket assembly and provided with a locking tooth plate, when the locking pawl piece is in the locked state, a locking pawl in the locking pawl piece and a locking groove on the locking tooth plate being locked and engaged, the rotating shaft and the bracket assembly being restricted from relative rotation by the locking tooth plate, when the locking pawl piece is at an unlocked position, the locking pawl in the locking pawl piece and the locking groove on the locking tooth plate being unlocked and disengaged, and the rotating shaft and the bracket assembly being rotatable relatively; and a rotating shaft resetting torsion spring connected to the locking tooth plate and the bracket assembly, the rotating shaft resetting torsion spring driving the locking tooth plate and the rotating shaft to rotate relative to the bracket assembly; wherein respective ends of the rotating shaft are adapted to be fixedly connected to ends of a pair of headrest support rods (51, 52); wherein the cam has a traction arm and a drive arm, the traction arm is connected to a headrest turnover unlocking cable, when the headrest turnover unlocking cable performs an unlocking operation, the cam is pulled by the traction arm to rotate around the cam shaft to further drive the drive arm to perform an unlocking operation, and the cam resetting torsion spring pulls, by the traction arm, the cam to rotate around the cam shaft to further drive the drive arm to perform a locking operation; wherein the drive arm has an unlocking arc surface and a first locking step surface, the unlocking arc surface being opposite to the locking step surface; and wherein the locking pawl piece is fixed on a pawl shaft, both ends of the pawl shaft are axially disposed on a first bracket wall and a second bracket wall, in addition to the locking pawl, the locking pawl piece also comprises an unlocking drive arm and a locking drive arm, the locking pawl is provided with a second locking step surface, the second locking step surface is coupled to the first locking step surface on the drive arm in the cam in a locked state, and an inner surface of the unlocking drive arm is coupled to the unlocking arc surface on the drive arm in the cam in an unlocked state. a bracket assembly; a rotatable cam axially disposed on the bracket assembly; a cam resetting component connected to the cam and the bracket assembly; a locking pawl piece axially disposed on the bracket assembly, the cam driving the locking pawl piece to move between a locked state and an unlocked state through forward and reverse movements; a rotating shaft axially disposed on the bracket assembly and provided with a locking tooth plate, when the locking pawl piece is in the locked state, a locking pawl in the locking pawl piece and a locking groove on the locking tooth plate being locked and engaged, the rotating shaft and the bracket assembly being restricted from relative rotation by the locking tooth plate, when the locking pawl piece is at an unlocked position, the locking pawl in the locking pawl piece and the locking groove on the locking tooth plate being unlocked and disengaged, and the rotating shaft and the bracket assembly being rotatable relatively; and a rotating shaft resetting torsion spring connected to the locking tooth plate and the bracket assembly, the rotating shaft resetting torsion spring driving the locking tooth plate and the rotating shaft to rotate relative to the bracket assembly; wherein respective ends of the rotating shaft are adapted to be fixedly connected to ends of a pair of headrest support rods (51, 52); wherein the cam has a traction arm and a drive arm, the traction arm is connected to a headrest turnover unlocking cable, when the headrest turnover unlocking cable performs an unlocking operation, the cam is pulled by the traction arm to rotate around the cam shaft to further drive the drive arm to perform an unlocking operation, and the cam resetting torsion spring pulls, by the traction arm, the cam to rotate around the cam shaft to further drive the drive arm to perform a locking operation; wherein the drive arm has an unlocking arc surface and a first locking step surface, the unlocking arc surface being opposite to the locking step surface; and wherein the locking pawl piece is fixed on a pawl shaft, both ends of the pawl shaft are axially disposed on a first bracket wall and a second bracket wall, in addition to the locking pawl, the locking pawl piece also comprises an unlocking drive arm and a locking drive arm, the locking pawl is provided with a second locking step surface, the second locking step surface is coupled to the first locking step surface on the drive arm in the cam in a locked state, and an inner surface of the unlocking drive arm is coupled to the unlocking arc surface on the drive arm in the cam in an unlocked state.