The utility model provides an indeterminate furnace roof, including the furnace roof casing, the foot encircles, the heat preservation, the insulating layer, anchor assembly is hung for at least two to the flame retardant coating, the furnace roof casing with encircle the foot welding together, hang anchor assembly one end weld in on the furnace roof casing, the heat preservation lay in on the furnace roof casing, the insulating layer lay in on the heat preservation, the pouring has the flame retardant coating on the insulating layer, it follows to hang anchor assembly the furnace roof casing is worn to locate in proper order the heat preservation the insulating layer with in the flame retardant coating. The utility model discloses a furnace roof casing still can continue to bear outer year through the load of encircleing the foot with hang anchor assembly dual mode support flame retardant coating after the part restraint is become invalid, and its stability and reliability are high.