This paper presents a two-scale method for the predictions of the effective coefficient of thermal expansion (CTE) of 4D-inplane carbon/carbon composite. The realistic finite element models of the carbon/carbon composite microstructure have been reconstructed through X-ray tomography images that directly include some of the microstructural features in the geometry such as the bundle imperfections, irregularly shaped voids, and bundle alignments. The localized behaviour of the composite has been studied under thermomechanical loads (from 27 °C to 2227 °C) at two scales namely; 1) micro-scale (where bundles are considered as a composite of fiber and matrix), 2) mesoscale (where bundles are considered embedded in the matrix to form a 4D carbon/carbon composite). The effect of the imperfection of the interface on the effective behaviour of CTE has been concluded using three conditions such as perfectly bonded, imperfectly bonded, and completely debonded. The CTEs have also been measured using experiments at mesoscale in in-plane (U-direction) and out of plane (Z-direction) directions over a range of temperatures from 200 to 2000 °C. The experimental data is used to validate the numerical predictions and it has found that the predicted behaviour of the effective CTEs over the entire range of temperature is in good agreement with the experimental observations.