The utility model discloses an automatic distance-adjustment mechanism for a coupling movable pulley block. Fixed pulleys are respectively connected via steel ropes below and above the coupling movable pulley block; the fixed pulley connected below is arranged on an angle-adjustable platform; a movable pulley frame is provided with a sliding component; the coupling movable pulley block realizes positioning and vertical sliding on a vertically-arranged pile frame guide rail via the sliding component; the movable pulley frame and the sliding component are connected via a connection rod; and two ends of the connection rod are respectively hinged with the movable pulley frame and the sliding component. When the ground tilts, the upper and lower steel ropes of the coupling movable pulley block are not on the same line, the connection rod rotates around hinge points at two ends of the connection rod to adjust the vertical distance between the coupling movable pulley block and the guide rail through the technical scheme of the utility model, and therefore the upper and lower steel ropes can be collinear, and the horizontal component force F generated by the non-collinear fact can be eliminated; and transverse compression or tension applied to the coupling movable pulley block and the pile frame guide rail can be effectively avoided, and reliability of hoist operation can be improved.