A filling pipe for use in high-temperature heat pipe filling operation includes an alkali metal filling unit, metallic pipe fixing unit, hermetic seal cover and stopping net. The alkali metal filling unit has a filling body, a receiving space disposed in the filling body. A feed inlet and a feeding pipe are disposed at the top and bottom of the filling body, respectively. A vacuum-generating component is disposed at the filling body laterally. The metallic pipe fixing unit has a fixing body and a taper opening disposed thereon and adapted to limit the metallic pipe. When the fixing body gets connected to the filling body, the feeding pipe is inserted into metallic pipe. The hermetic seal cover covers separably the feed inlet. The stopping net is movably disposed in the receiving space. Therefore, solid alkali metals are filled into a metallic pipe easily and safely.