In natural gas treatment, sulfur recovery unit can recover H2S gas generated in sulfur removal unit and make it form sulfur. Sulfur recovery unit has such characteristics as high H2S content and high temperature and it is necessary to set refractory lining inside the unit. In certain key overseas project of PetroChina, it is found that refractory lining of reheating furnace and tail gas incinerator in sulfur recovery unit has too low compressive/rupture strength at normal temperature. Through visual inspection, rebound hammer test, mechanics test, model test and theoretical analysis, considerations are proposed in design and construction of heavy casting materials, which has certain guiding significance for refractory lining material selection in future.