The utility model discloses a runner unit, including interior casing and the shell body that is the tubular structure, the both ends of interior casing are fixed with flange respectively, the shell body cover is in outside the interior casing and with two flange is fixed, just the shell body with interior casing is the interval and sets up, interior casing, shell body and two form the confined waterway between the flange. This runner unit passes through flange and forms complete flue gas runner with other runner units, need to dismantle only need when changing with the flange of butt joint divide open can, the maintenance of being convenient for. And be formed with the waterway between the inner/outer casing body, the heat of the internal flue gas of inner shell can be taken away to the cooling water that flows in the waterway for the heat dissipation improves the heat resistance and the thermal -insulated nature of runner unit, is favorable to prolonging the life of runner unit. Correspondingly, the utility model also discloses a high temperature resistant flue gas runner of novel double -layered shell type that comprises a plurality of runner units.