[en] A new materials-genome-based multiscale modeling method is proposed to predict the thermal conductivity of SiC/SiC composites subjected to neutron irradiation. The modeling method bridges different scales from the atomic scale to the macro scale of a 2D SiC/SiC composite. The irradiation-induced point defects in the interphase of SiC/SiC composites are first studied using molecular dynamics simulations to compute the degradation of thermal conductivity as a function of irradiation dose and temperature. The thermal conductivities of SiC fibers, matrices and interphase are then used as input for the new materials genome model to compute the thermal conductivities of 2D SiC/SiC composites subject to neutron irradiation. The predicted thermal conductivities for both unirradiated and irradiated SiC/SiC composites are found to decrease with an increase of temperature while the irradiation effect on interphase needs to be considered for irradiated SiC/SiC composites.