Based on Eshelby equivalent inclusion principle and multi scale nature of the microstructure of cement based composites(CBCs), the micromechanical approach to evaluate the thermal properties of the CBCs was employed. A generalized multi scale micromechanical model was developed to calculate the thermal conductivity of the CBCs. Mori Tanaka homogenization method was adopted to upscale the thermal conductivity of CBCs of different compositions, water cement ratios and curing ages. Then, the effect of saturation degree was assessed by the model. The modeled results are comparable to the data from experimental measurement, suggesting that the multi scale micromechanical model developed is available to predict the thermal conductivity of CBCs in different saturation degree. Furthermore, this approach can also be extended to calculate other thermal parameters of CBCs of complex compounds and curing schemes.