The change of the internal stress of dense refractory castables during unilateral rapid heating was studied by the electric stress measurement. The results indicate that: (1) during rapid heating, the position near the heated surface is under compressive stress; the closer the position to the heated surface, the larger the compressive stress; (2) the specimen bursts during the rapid heating; (3) the calculated stress of the structure at the burst moment shows that the compressive stress produced at the same depth as the cracking surface exceeds the ultimate strength of the structure.