In casting large castings, the rational use of refractory hollow tube sprues has great advantages. The casting temperature is reduced slowly, keeping the alloy liquid into the cavity temperature, the heat preservation property is good, the heat transfer of the alloy liquid to the dry sand is reduced, the relative heating is maintained and the casting temperature is maintained, so that the alloy liquid is smoothly filled and the back spray phenomenon is avoided. The sprue of large bed castings has a large cross section and high height, especially in a certain temperature range, which often produces back spray, which can be avoided with refractory sprues. Overcoming the falling sand, there is no white film at the upper end of the sprue gate under the sprue cup, and there is no white film at the joint between the sprue and the sprue. Therefore, the dry sand which has lost the sand, falls sand, and washed the sand and appears white spots enters the casting.