This application discloses a seat backrest lock structure, including a seat base frame and a backrest frame. A
locking mechanism is located on the lower side of the backrest frame, and an unlocking mechanism is located in the middle of the lower part of the backrest frame. The locking and unlocking mechanisms are connected by a detachable pull cable. The
locking mechanism includes a fixed
bushing, a stop pin, and an elastic element. The fixed
bushing passes through the lower end of the side rod of the backrest frame. The stop pin reciprocates within the fixed
bushing in cooperation with the elastic element. The base frame has a stop hole, into which the stop pin extends to secure the backrest frame. The unlocking mechanism includes an adjusting
handle, a stepped screw, a pull cable fixing plate, and a reset elastic element. The stepped screw connects the adjusting
handle and the pull cable fixing plate. When the adjusting
handle is rotated around the stepped screw as a pivot, the stop pin can be pulled out of the stop hole to unlock the backrest lock. This application increases the structural strength of the seat frame while simplifying the backrest lock structure, simplifying the overall seat unlocking structure, resulting in high strength, low cost, and improved user experience.