Prefabricated directly-buried fixing joint for steel-jacket-steel thermal insulation pipe fitting

The utility model relates to a steel jacket steel thermal insulation pipe fitting prefabricated direct burial fixing joint which comprises a working pipe, a reducing pipe assembly and an outer protective pipe, a thermal insulation layer is arranged in a thermal insulation jacket between the working pipe and the outer protective pipe, and the reducing pipe assembly comprises an inner reducing pipe and an outer reducing pipe. The large end of the inner reducing pipe is connected with the small end of the outer reducing pipe through a via hole sheath by using a locking bolt, an air pressure hole is formed in the reducing pipe assembly, an outer sleeve protective layer is clamped and sleeved on the outer side of the welding position of the outer reducing pipe and the outer protective pipe, moisture removal pipes are welded on the side walls of the outer protective pipe on the two sides of the outer reducing pipe, and protective sleeve protective layers are clamped and sleeved outside the moisture removal pipes. A