Backrest anti-shearing device

The invention discloses a backrest shearing force preventing device which is suitable for a backrest with an angle adjusting function and comprises a basic backrest and a sliding backrest. Relative sliding between the basic backrest and the sliding backrest is realized through a sliding piece; a counterweight traction mechanism is arranged on the basic backrest, a traction fixing mechanism is arranged on the sliding backrest, and the counterweight traction mechanism is matched with the traction fixing mechanism and used for adjusting the height of the sliding backrest. Through the sliding piece and the counterweight traction mechanism, relative sliding of the back of the human body and the seat backrest is converted into sliding of the sliding backrest relative to the basic backrest, relative displacement of the back of the human body and the sliding backrest does not exist, discomfort of the back is relieved, the risk of friction damage is avoided, and meanwhile the risk that the body slides forwards can be