For devices based SiC epitaxial technology to function satisfactorily, the lattice parameters, perfection, thickness and roughness of the epilayers must be accurately controlled. Xray diffraction is one of the most powerful and widely used techniques for this aim. In this papaper, we introduce a series of advanced X-ray diffraction/scattering techniques, including double-axis diffraction, multiple-order reflections, triple-axis diffraction and reciprocal space mapping, for characterization of SiC epitaxial structures. These techniques are capable of extracting very detailed structural information of SiC homo- and hetero-epitaxial systems, such as accurate lattice parameters, lattice mismatch and misorientation, polytype identifications, dopant concentration, layer thickness, and lattice perfection. The application of these techniques to measurements of small lattice mismatch or misorientation in 3C/4H and 3C/6H SiC heterostructures and in highly doped hornoepitaxial 4H SiC epilayers are demonstrated.