The utility model provides an online prosthetic devices of dry coke quenching high temperature metal expansion joint, belongs to coking equipment repair tools technical field. Its technical scheme is: two semicircles seal up the upper end of snap ring difference welded connection at two semicircle seal guide sleeve, the connecting flange is with two semicircle sealed snap rings, the seal guide sleeve hookup is as an organic whole, go up sealing ring, the carbon fibers packing is placed between the pipe of the upper end of the circumferential inner wall of sealed snap ring and high temperature metal expansion joint, two semicircle seals are arranged in the circumferential inner wall of two semicircle seal guide sleeve lower extremes respectively, place the carbon fibers packing between seal guide sleeve circumferential inner wall and seal, sealing ring and carbon fibers packing have been placed down between the lower extreme pipe of seal and high temperature metal expansion joint. The utility model discloses can be to leaking online whole restoration of high temperature metal expansion joint, guarantee the sealed effect of system under the various pressure operating modes of high temperature, and satisfy former expansion joint each to the compensation requirement, avoid completely stopping production and overhaul the loss that brings production and equipment.