The invention relates to a generator technology, and discloses a large-capacity air-cooled generator stator in-slot fixing device. The large-capacity air-cooled generator stator in-slot fixing devicespecifically comprises a stator core, a stator coil, a side gasket and corrugated plates, wherein the stator core is provided with a coil inserting slot, the side edge of the coil inserting slot is provided with expansion slots, the stator coil is placed in the coil inserting slot, the side gasket is plugged between the stator coil and the stator core, and the corrugated plates are respectively driven into the expansion slots. The invention further discloses an implementation method of in-slot fixation, which comprises the steps of first, fabricating expansion slots in a coil inserting slot ofthe stator core, driving a process inclined wedge at the position of each expansion slot after the stator coil is inserted, wedging the coil to be upright in position and wedging the coil to the other side of the coil inserting slot; second, plugging a first gasket into a gap between the expansion slots, and then plugging out the process inclined wedges; and third, driving a corrugated plate anda second gasket at the position of each expansion slot. The large-capacity air-cooled generator stator in-slot fixing device enables the stator coil to be good in heat conduction with the core while being firmly fixed in the slot, and the stator coil can also perform axial thermal expansion in the core.