The utility model relates to a double -fed variable speed constant frequency hydraulic generator's air runner, cooling air carries out the heat exchange at the in -process that each flow region flows with parts that generate heat such as rotor core, stator coil, collecting rings, takes away the loss heat of the part that respectively generates heat, and the temperature of the part of ensureing respectively to generate heat is in security range. The rotor air duct adopts the duct spacer bearing structure the same with the stator air duct, make full use of the high -speed rotatory pressure head effect that produces of rotor tip coil, improved the air total flow, the great swirl of formation has designed the deep bead the rotor tip coil near in order to avoid simultaneously, open the problem that stress concentration had not only been solved to the exhaust vent on founding the muscle crown plate, still increased the effective height of cooler, make the cooling water take away more loss heat, reduced cooling air's temperature, more be favorable to electric machine cooling. Can satisfy variable speed hydraulic generator's cooling demand completely.