Abstract: The driving gear box of the cutting part is the main working part of the anchor excavator in the underground excavation roadway.Its failure will cause the machine and production to stop, not only affecting the progress of the tunneling project, resulting in a waste of repair costs, but also a great safety risk when replacing the gear box of the cutting part, resulting in unpredictable losses in the coal mine.In view of the faults in the process of using the gearbox, a professional QC team has been established to carry out analysis and calculation.By adopting such scientific quality control methods as association diagram, 5M1E and orthogonal test, we finally find out the two fundamental reasons for the unreasonable floating seal oil leakage of the shell and the seal structure of the input shaft end.Corresponding measures have been taken for reasonable control and prevention, and the proportion of faults has been controlled to a reasonable level, so as to ensure the normal production of the working face of underground tunneling, reduce the occurrence of safety accidents when replacing large parts, and improve the maintenance quality and reliability.