Abstract: This paper studied the damage failure mechanism of fiber-reinforced ceramic composites under unidirectional loading. According to the conventional shear-lag model, Coulomb’s law was introduced to describe the interfacial shear stress. According to the energy balance method and the debonding criterion of fracture mechanics, the steady-state cracking stress of the matrix and the debonding length of the interface were calculated. The difference and applicable range of the steady-state cracking stress of the matrix under different shear lag models were analyzed, and the effects of the interfacial shear stress, the interfacial friction coefficient, the interfacial debonding energy, and the fiber volume fraction on the steady-state cracking stress of the matrix were discussed. The shear lag model was used to describe the microstructure stress field of the fiber-reinforced ceramic composites after damage, the distance between the matrix cracks was determined according to the random evolution method of matrix cracks, and the debonding behavior of the interface was described according to the fracture mechanics debonding criterion. Combined with the damage model, the stress-strain curve of unidirectional fiber-reinforced ceramic composites under unidirectional load was predicted, and the influence of various factors on the stress-strain curve was discussed.