The invention relates to an on-line replacing method for an extrusion roll of a fiber spinning traction feeding machine, in particular to the on-line replacing method for the extrusion roll of the traction feeding machine in the dry-method spinning process of acrylon, belonging to a fiber spinning conveying device. The on-line replacing method is characterized in that: when the extrusion roll hasfaults, an extrusion device special for maintenance is used to temporarily replace the extrusion function of the traditional extrusion roll having faults to maintain the normal operation of the fiberspinning traction feeding machine; and according to the extrusion device special for maintenance, a tray 4 on which an extrusion roll 1 special for maintenance is fixed penetrates through a fixed bolt groove in the middle of the tray through a tray fixing bolt 6 and is fixed on a traditional serially-connected roll shaft seat, thus the operation for on-line replacement for the extrusion roll can be finished and the aim of the on-line replacement for the extrusion roll can be achieved. The invention provides the method for realizing the on-line replacement for the extrusion roll of the traction feeding machine under the state of maintaining the normal operation of the fiber spinning production device; and the on-line replacing method is suitable for the one-line replacement of the extrusion roll of the traction feeding machine for the fiber spinning device using belt clamping force conveying equipment.