Slag corrosion is one of the main damage modes for refractory castables used in iron and steel metallurgy. The matrix plays vital roles for corrosion resistance of refractory castables. In the present paper, the properties of the Al2O3‐SiC‐C‐based trough castables with in situ carbon containing calcium aluminate cement (CCAC) and ball pitch as carbon sources, respectively, were comparatively investigated. The microstructures of the trough castables after corrosion were observed by field‐emission scanning electron microscopy. The results showed that after being corroded at 1450°C for 3 hours, the corrosion depth of Al2O3‐SiC‐C‐castables with CCAC as binder (A2) was 1.2 mm, 65.71% lower than that of the trough castables with ball pitch as carbon source (A1), though the content of carbon materials in the former was much lower than that of the latter. The reasons for these observations were that the in situ carbon materials of CCAC exhibit improved distribution in the matrices of castables and excellent oxidation resistance, resulting in lower porosity within the castables, and hindered the penetration of the molten slag at high temperatures. In addition, the Al2O3‐SiC‐C‐castables bonded by CCAC displayed good mechanical properties at room temperature and elevated temperature.