The invention discloses a coalbed gas well casing repairing method, and belongs to the technical field of coalbed gas well repair. The coalbed gas well casing repairing method comprises the following steps: putting down a well dredging pipe column into a casing for well dredging; in the process of putting down the well dredging pipe column, and when meeting an obstructing point, taking out the well dredging pipe column; grinding and milling a dislocated or broken position of the case by using a grinding and milling pipe column so as to put down the grinding and milling pipe column into the bottom of a coalbed to be repaired; putting down a repairing pipe column into the coalbed to be repaired, wherein the repairing pipe column comprises a first oil pipe, and an expandable cone and an expandable screen pipe which are connected with the first oil pipe; pressurizing the expandable cone so as to enable the conical surface of the expandable cone to support the inner wall of the expandable screen pipe, and outwardly expand the expandable screen pipe to tightly adhere to the inner wall of the casing. By the coalbed gas well casing repairing method, the problems that repairing steps are complex and production needs of a coalbed gas well after repairing cannot be met are solved; complex construction steps are simplified; after repairing, a well shaft is high in strength and better in stability, and the production needs of the coalbed gas well are met. The coalbed gas well casing repairing method is used for repairing the coalbed gas well casing.