Calcium aluminate cement bond reacts with matrix to form flake calcium hexaluminate phase at a high temperature, thus effectively improving the thermal shock resistance of the material. However, too much cement will produce a large volume expansion that affects the properties of the material. In this paper, calcium hexaluminate aggregate was used to partially or completely replace the tabular corundum aggregate to prepare castable, and the effect of aggregate porosity on the mechanical properties of castable after curing and high-temperature treatment was investigated, and the fracture behavior of castable was analyzed via wedge splitting experiment. The results show that at 25 ℃, compared with tabular corundum, water absorption and release effect of pores in calcium hexaluminate aggregate promote the formation of more hydration products around the aggregate, accelerate the hydration reaction of cement, and favor the interface meshing between aggregate and matrix. After heat-treatment at 1 600 ℃, the hydration product is transformed into a secondary phase CA6, which improves the interface strength of aggregate and matrix, and increases the proportion of crack propagation in aggregate during material fracture. The castable with 30%CA6 aggregate has an optimum crack propagation resistance.