4H-SiC single crystal with a diameter of 1.5'' has been grown by the seed sublimation method. Regions of mixed polytypes are assessed by high resolution X-ray diffractometry with the asymmetrical diffraction geometry. Multiple reflections are observed from the rocking curve measurements of a longitudinal cut 4H-SiC slice. Those reflections are indexed to be 2131 and 2131 of 4H-SiC, 2130 , 2131 , 2131 , 2132 and 2132 of 6H-SiC, 2131 , 2132 , 2134 , 2135 and 2137 of 15R-SiC respectively based on the lattice constants of different polytypes in SiC crystal. It is believed that the polytypes can be identified by high resolution X-ray diffractometry.