Some dislocations, which are generated in the diamond single crystal during the diamond crystal growth from Fe-Ni-C system, may affect diamond crystal growth mode at high temperature-high pressure (HPHT). The concentricdiamond single crystals were observed by scanning electron microscopy (SEM). The concentric dislocation loopsformation process and their effect on the diamond crystal growth mode were analyzed. It should be noted thatwhatever the nature of the dislocation is, should the Burgers vector of dislocation has a component at the directionnormal to the growth interface, the dislocation will make the face parallel to the growth interface grow into spiralface. The presence of consecutive spiral steps on the diamond crystal surface also provides a direct evidence of thedislocation mechanism of diamond crystal growth.