The invention relates to a gas power nail gun, belonging to the technical field of gas power tools. The lower part of a cylinder body in a casing of the nail gun is fixedly connected with a nailing seat; a bunting head is installed at the lower part of the nailing seat; an extending flange and guide grooves are respectively arranged at two sides of the cylinder body; a left bunting arm and a right bunting arm are respectively embedded in the guide grooves at two sides; the upper end surfaces of the bunting arms are connected with the extending flange through a bunting arm spring; vertical slide rails are arranged at two sides of the nailing seat; a gun nozzle and a guide tube are installed at the lower end; a guard board inner wall and a guard board which are vertical to positioning planes are respectively extended on the positioning planes of two sides of the upper end of the bunting head; the guard board inner wall and the guard board are connected by inner wall steps; the guard board inner wall and the nailing seat form a moving pair; the lower ends of the left bunting arm and the right bunting arm are respectively provided with inner walls; and the lower end surfaces of the inner walls are abutted on the corresponding inner wall steps. The invention has simple structure, material saving and economic cost, and the parts are mutually tenoned and embedded into a whole after assembling, thus ensuring that the left bunting arm and the right bunting arm are under balanced stress.