A method of cooling a vane of a turbine is provided. The turbine includes an airfoil, an outer shroud disposed at an outer radial end of the airfoil and an inner shroud, the airfoil including a plurality of air channels extending along the radial direction of the turbine, the air channels comprising a first air channel and a second air channel. A cooling air is caused to flow inside the first air channel to cool the first air channel, then cool one of the outer shroud and the inner shroud. A cooling air is caused to flow inside the second air channel to cool the second air channel, then cool the other one of the outer shroud and the inner shroud.