Aerospace vehicles are exposed to a high temperature environment by aerodynamic heating during re-entry. A thermal protection system (TPS) such as ablator is required to protect the spacecraft from this environment. In previous studies, porous carbon ablator (hereafter denoted as PCA) composed of three-dimensional networked porous carbon (here after denoted as TNPC) substrate and resin with a low residual carbon ratio is fabricated. An experimental performance of PCA is performed by arc-jet test and recession behavior is evaluated. Although the experimental evaluation on TNPC and PCA have been conducted, analytical evaluation is not established well. In the present study, the heat conduction analysis of TNPC and PCA is performed by finite element method. Thermal and mechanical properties of TNPC and PCA is obtained by experiments. As a result, the analytical results are generally in agreement with the experimental values. From the obtained temperature distribution, the thermal stress distribution is also evaluated. The result suggests that the design of ablator for the decrease of not only heat conduction, but also internal stresses are required.