The diamond single crystal, synthesized with Fe-Ni-C-B system of catalyst under high temperature and high pressure, had been observed by field emission scanning electron microscope and transmission electron microscope. The presence of a cellular structure suggested that the diamond grew from melted catalyst solution and there existed a zone of component supercooling zone in front of the solid-liquid interface. The main impurities in the diamond crystal was (FeNi)(23)C-6. The triangle screw pit revealed on the (111) plane was generated by the screw dislocation meeting the diamond (111) plane at the points of emergence of dislocations. A narrow twin plane was formed between the two (111) plane. (C) 2013 Elsevier B.V. All rights reserved.