Telescopic tensioning mechanism, telescopic tensioning method and inner and outer nested mast

The invention discloses a telescopic tensioning mechanism, a telescopic tensioning method and an inner and outer nested mast, the telescopic tensioning mechanism comprises a movable pulley block which is connected to an inner mast in a sliding mode in the axial direction of the inner mast and a fixed pulley fixed to an outer mast, and one end of a steel wire rope is fixed to the outer mast; the other end is fixed at the lower part of the inner mast by bypassing the fixed pulley and the movable pulley block; a second chain wheel is fixed at the upper part of the inner mast, a third chain wheel is fixed at the lower part of the outer mast, a fourth chain wheel is slidably connected at the lower part of the outer mast along the axial direction of the outer mast, one end of a guide chain track of the working device is fixed on the inner mast, and the other end bypasses the movable pulley block, the second chain wheel, the third chain wheel and the fourth chain wheel and is fixed on the outer mast; the connecting