A precise measurement, which was based on the automated grid method, was developed to analyze the mechanical properties of a three-dimensional reinforced carbon/carbon composite under tensile and shear loading conditions. Young’s moduli and Poisson’s ratios of the carbon/carbon composites were studied by means of unidirectional tension testing, and the shear modulus was measured using the Iosipescu shear testing technique. The contact measurement method also was applied to test the tensile strain, and a more sophisticated method based on the digital image correlation technique was applied to test the shear strain. All the testing results obtained from the different methods agree well with one another, and the analysis indicates that the automated grid method is appropriate for testing the mechanical properties of carbon/carbon composites. Based on the stress state analysis, the Young’s modulus along the wrap or weft fiber orientations of the carbon/carbon composite can be obtained via the Iosipescu shear test.