The steel strip of the main bearing of TB880E tunnel boring machine (TBM) is worn out by the lip seal. Then the steel strip breaks and pierces the seal, which results in the failure of the seal system. Under such circumstance, a large amount of dusts and other particles enter the main bearing. Therefore, the seal system of the main bearing needs to be repaired. The cutter head of the TBM is dismantled in the tunnel, the seal of the main bearing is removed, the lip seal and the wearresistant steel strip of the main bearing are replaced and the labyrinth seal is repaired. The practice demonstrates that that, even in confined space, the repairing of the seal system of the main bearing can be fulfilled efficiently by optimizing the traditional repairing techniques and adopting innovative repairing process. 