The mechanical behaviors of silica-based cores for the directional solidification of single crystal superalloy hollow blades were investigated. The experimental results of strength, elastic modulus and stress-strain relationship of sintered samples S0 and heat treatment samples S1, S2 and S3 were obtained. Based on the Weibull distribution statistics, the continuous damage constitutive model of silica-based cores for the directional solidification of single crystal superalloy hollow blades was established by using M-C (Mohr-Coulomb) criterion. The method of determining the relevant parameters of the continuous damage constitutive model was given. The results show that the mechanical properties and the degrees-of-sinter of silica-based core samples with heat treatment at 1500℃ are improved. The relationship between the crack propagation and the macroscopic fracture of silica-based cores is described by using the damage variable D in the constitutive model and microstructure.