The purpose of this study is to confirm that the out-of-plane coefficient of thermal expansion (CTE) of CF/Epoxy plain weave composite is larger than that of UD composite by numerical analysis and experiment, and to clarify its reason and mechanism. Plain-weave composite with fiber volume fraction (Vf) of 51.6% is used as test specimen. The fiber and base resin of specimen is T-300 and XNR6813/XNH6813, respectively. The experiment is conducted by thermomechanical analysis (TMA). Experimental result shows that the out-of-plane CTE is 6.51×10-5 K-1 and it is about 10% larger than that of UD composite. Because the standard deviation is less than 1%, it is also confirmed to obtain it with good accuracy. The analysis is executed by the homogenization method and 3-D finite element method (FEM). FEM analysis shows that the difference between it and experimental result is 10%, and it becomes the same tendency as experimental result, it is confirming that out-of-plane CTE is larger than that of UD composite. To investigate the mechanism of large CTE, further analysis is executed. Analytical results show that the expansion by thermal residual stress accounts for about 30% of overall thermal expansions. Therefore, it is proven experimentally and analytically that out-of-plain CTE of CF/Epoxy plain-weave composite is very large.