The thermal conductivity of cement paste with different water-cement ratios and curing ages were measured. Moreover, the thermal conductivity of cement paste was predicted by parallel model, series model, Maxwell model, MT model, EMT model and SC model, respectively. In addition, the thermal conductivity of each phase in cement paste was calculated by a molecular dynamics method. The results show that the thermal conductivity of cement paste decreases with the increase of curing age and water-cement ratio. SC model can be used to predict the thermal conductivity of cement paste at different water-cement ratios or curing ages, and the relative error between the predicted and the experimental values is 0.3%-4.7%. The Maxwell model and MT model can be used to calculate the thermal conductivity of cement paste at a large water-cement ratio and a long curing age.