The cause of left foot swelling after lumbar slip surgery may be poor venous return of the left lower limb, venous thrombosis and so on. 1. Poor venous return of the left lower limb: the left lower limb may be compressed during lumbar slip surgery, or the left lower limb is inactive for a long time, so that the venous return of the lower limb is poor, resulting in the obstruction of the tissue fluid return and the swelling of the left foot, which can be recovered gradually through the activities in general. 2. Venous thrombosis: during lumbar slip surgery, the muscles of the lower limbs lose their contraction function due to anesthesia, and the muscles of the lower limbs are in a state of relaxation due to postoperative bed rest, which causes venous thrombosis in the lower limbs, and the emergence of thrombosis requires urgent treatment. There may be other reasons for the swelling of the left foot after lumbar slip surgery, which should be consulted in time, and the doctor should determine the specific cause of the disease according to the symptoms, signs and auxiliary examination, and give treatment according to the cause of the disease.