Abstract: A promising method of planar array electrical capacitance tomography(ECT) for thermal protection materials nondestructive detection is presented. This method can detect targeted object only from a limited access. In this study, a planar ECT system with 12 electrodes has been developed for experiment and its simulation model also has been built by using ANSYS. The sensitivity matrix is essential and fundamental in the process of image reconstruction. To optimize the sensitivity matrix, the influences of permittivity of sensitive filed and selection of section for reconstruction image have been discussed. The experimental results show that there exist great differences in reconstruction images for different sections and the image quality of the second layer is the highest, whereas the change of permittivity has little influence on detection results.