The invention relates to a heat-insulation structure for end part of radiant tube used for industrial furnace heating. The end part of the radiant tube is clamped in a pair of mutually-buckled rectangular ceramic fiber modules; tube grooves are formed in a plane where the ceramic fiber modules are in mutual contact along the longitudinal directions of the modules in a digging manner, wherein one section of each tube groove is a semi-circular hole; when the two ceramic fiber modules are buckled, the two tube grooves are combined into a circular hole and contain the end part of the radiant tube in the circular hole; the radiant tube extends into a furnace body and is fixed with the furnace body in a welding manner; a heat insulation part at the end part of the radiant tube provided with the ceramic fiber modules is in contact with a heat insulation layer in the furnace body; and the ceramic fiber modules naturally expand along the width direction and are filled into a gap between the radiant tube and the heat insulation layer in the furnace body. The heat-insulation structure has the benefits that the treatment problem of the gap between the heat insulation part at the end part of the radiant tube and the furnace body can be easily solved, the heat conduction and the furnace casing temperature in the position are ensured, the heat loss is reduced, and the operating environment is effectively improved, and meanwhile, the bricklaying construction in an irregularly-shaped furnace is also avoided.