The invention relates to a method for retreating a main bearing of a tunnel boring machine. The method comprises the following steps that (1) the tunnel boring machine is tunneled to a stabilizing surrounding rock to form the tunnel face; (2) all hobs on a cutterhead are removed, and construction layout of a cutterhead reinforced pre-stressed anchor cable, a cutterhead supporting embedded part anda big gear ring containing side hole is carried out at the tunnel face; (3) the tunnel boring machine is retreated from the tunnel face to the predetermined position; (4) surrounding rock support iscompleted at the predetermined position; (5) the cutterhead reinforced pre-stressed anchor cable and the cutterhead supporting embedded part are manufactured and installed, and the big gear ring containing side hole is excavated; (6) the cutterhead reinforced pre-stressed anchor cable is connected to the cutterhead, and the pre-stressed anchor cable is tensioned to the fixed position and locked; and (7) an operating space which can be used for replacing tunnel boring machine (TBM) fittings such as big gear rings is formed between the cutterhead and the main bearing. The method has high construction efficiency and is low in construction cost.