Cooling runner structure in three-layer shell steam turbine and steam turbine

The invention provides a cooling runner structure in a three-layer-shell steam turbine and the steam turbine. The cooling runner structure is applied to the three-layer-shell steam turbine. The three-layer-shell steam turbine comprises an outer shell, an outer shell, an inner shell, a steam inlet chamber and a rotor, the outer shell wraps the periphery of the inner shell, and the outer shell wraps the periphery of the outer shell; the steam inlet chamber is arranged in the inner shell, and a steam through-flow expansion channel is arranged among the inner shell on one side of the steam inlet chamber, the outer shell, the inner shell and the rotor. The steam inlet chamber is provided with the first flow channel, the second flow channel, the third flow channel and the fourth flow channel, temperature difference and pressure difference loads borne by the inner shell and the outer shell are reduced by means of the difference between steam parameters of the first flow channel (the second flow channel) and steam pa