The thermal shock resistance of mullite castable with different steel fiber contents (i.e., 0-2.5% (mass fraction)) was evaluated by a wedge splitting method and a thermal stress factor. The thermal shock resistance of the castable was also analyzed by three different thermal shock resistance characterization methods (i.e., the residual ratio of modulus of rupture, modulus of elasticity and ultrasonic wave velocity in air at 1 100 ℃. The results show that the fracture energy (R'''') and fracture toughness increase with the increase of steel fiber content from 1.0% to 2.0%, thus improving the thermal shock resistance of castable. The rapid generation and propagation of cracks can lead to a decrease of R'''' and thermal shock resistance when the addition of steel fiber exceeds 2.0%.