A device and a method for reducing wind resistance power of a large geotechnical centrifuge are provided. A semicircular tube cylindrical cooling device is provided between an internal side of a high-speed rotor system and a cylindrical shell. A serpentine top semicircular tube cooling plate is provided right above a hanging basket, and return helium gas inlet holes are provided at a center of the top semicircular tube cooling plate. A helium gas in a helium gas storage tank passes through helium gas outlets on the helium gas inlet pipes, and enters a centrifuge chamber from a bottom sealing plate. The helium gas is used to replace air in the centrifuge chamber to reduce the wind resistance power and corresponding energy consumption. No vacuuming is required, so sealing requirements are lower. Heat dissipation equipment is placed inside the centrifuge chamber, and a helium gas circulation wind duct is added.