The dislocations in cc-SiC single crystal are studied by means of etching method and X-ray topographic method. The etchant used is the fused alkali hydroxide. The one-to-one correspondence between the etch pits with sharp bottom and the dislocations are confirmed. Because of the Burgers vector of the screw dislocations in [0001] direction are much larger than that of the edge dislocations, one can distinguish the screw dislocations from the edge dislocations according to the depth of etch pits. The correspondent relation between the shape of etch pits and the crystal structure of polytype is given. The relationships between the pattern of growth spiral on surface and the dislocations as well as the movement of dislocations are studied. X-ray topography shows that a lot of dislocations in cc-SiC are on the base plane (C plane). The growth dislocations nucleate at the crystal root and extend along the direction of crystal growth passing through the whole crystal in the crystal growth process, so the dislocation lines are always along the [1010] and [1120] direction. The dislocations in cc-SiC crystal can be observed completely only when both the etching method and X-ray topographic method are employed.