The invention discloses a fixed-point gas outlet method, and belongs to the technical field of power system lightning protection. A fixed-point gas outlet device is arranged. The fixed-point gas outlet device comprises a steel shell. A gas-producing fuel is placed in the steel shell. One end of the steel shell is provided with a trigger pin. The trigger pin penetrates through the steel shell to contact with the gas-producing material in the steel shell. The other end of the steel shell is provided with a gas outlet part. The shell at the gas outlet part is thinner than the shell at other partsof the steel shell. The wrapping strength of the steel shell is greater than the maximum atmospheric pressure of the gas-producing material. The lightning trigger signal contacts the gas-producing material after passing through the trigger pin. The gas-producing material in the steel shell instantly burns to generate arc-extinguishing gas. The arc-extinguishing gas breaks through the shell at thegas outlet part, and the arc-extinguishing gas ejects out from the gas outlet part to extinguish the arc. The method can improve the safety capability of the solid phase arc extinguishing lightning protection device without damaging the external structure under the condition that the external structure is not strengthened.