The invention discloses a gas reverse-circulation well-drilling method. According to the gas reverse-circulation well-drilling method, a well-drilling system comprising a well-drilling pump set, a topdrive, a top drive adapter, a rotary blowout-preventing flow guiding device, a blowout preventer group, a casing, a double-wall drill pipe, a flow channel conversion device, a conventional drilling rig and a drill bit is used; and the gas reverse-circulation well-drilling method comprises the steps that during gas injection and well-drilling, one path of injected gas passes through the top drive,the top drive adapter, the double-wall drill pipe, the flow channel conversion device, the conventional drilling rig and the drill bit to enter a well bottom annular space, the other path of the injected gas enters the well bottom annular space through the rotary blowout-preventing flow guiding device; and the two paths of injected gas converge in the well bottom annular space and then passes through the flow channel conversion device, the double-wall drill pipe and the top drive adapter to return to a grit chamber. The gas reverse-circulation well-drilling method has the advantages that thegas using amount is small, the drilling speed is high, and low-cost well drilling can be achieved; and the gas reverse-circulation well-drilling method meets the well-drilling well control and well-drilling safety requirements in the field of oil drilling.