The invention discloses a pneumatic control weight reduction supporting system, and belongs to the technical field of medical rehabilitation equipment. The system can control a tension value in a certain range to realize constant tension control. The system comprises a stand with pedestal, and is characterized in that the stand is provided with a first fixed pulley and a second fixed pulley, wherein the pedestal of the stand is provided with a cylinder; a piston rod of the cylinder is provided with a movable pulley; the pedestal on the two sides of the cylinder is provided with a third fixed pulley and a fourth fixed pulley respectively; a winch is arranged in a lateral direction of the fourth fixed pulley; a back strap arranged below the stand is connected with the winch through a force sensor, the first fixed pulley, the second fixed pulley, the third fixed pulley, the movable pulley and the fourth fixed pulley by a connecting rope in turn; a position sensor is arranged on the cylinder; the cylinder is connected with a pressure sensor and a pneumatic control valve respectively; the pneumatic control valve is connected with an air pump station; and the force sensor, the position sensor, the pressure sensor, the pneumatic control valve and the winch are connected with a computer respectively.