Abstract: The object translation often occurs between the serial images，which are captured at different analyzer positions in the polarized light microscopy for determining the extinction angle (Ae) of pyrocarbon in C/C composites. The translation results in the incorrect Ae value. An image registration algorithm based on structure features was proposed for translation correction. A circular template was used in the algorithm to detect the centre of the same fiber circular section in each image as a matching point. The image registration was realized through coordinate transform. The proposed algorithm has been applied to the Ae measurement of pyrocarbon. The experiment result shows that the image registration can avoid the wrong sampling data caused by object translation and assure Ae measurement accuracy.