The utility model discloses a backrest folding structure for a child dining chair. The seat comprises a seat body and a backrest, a rotating shaft and an elastic movable unfolding buckling part are arranged between the seat body and the backrest, the seat body and the backrest are matched in a rotating unfolding or rotating folding mode through the rotating shaft, and unfolding positioning is achieved through the unfolding buckling part at least when the seat body and the backrest are mutually rotated and unfolded to a certain position. Through the improvement of the structure, the occupied position of the dining chair can be effectively reduced, the backrest of the dining chair can be folded and stored by a user when the dining chair is not used, and the dining chair has the advantages ofbeing simple and reasonable in structure, excellent in performance, rapid in folding, convenient to use, low in manufacturing cost, easy to produce, easy to achieve, small in size, safe, reliable andthe like, and is high in practicability.