Abstract: For accurate judgment of the black fringe defects found by macroscopic test in TC6 titanium al-loy bar,the microstructure of the alloy bar was firstly observed by metalloscope to locate the defects,then the defects were characterized by SEM,which shows that the black fringe areas are caused by segregation with higher content of Mo and lower content of Al in comparison to those of the normal areas.The micro-hardness testing was carried out,and the defects were determined to be non-brittle segregation.The re-sults show that the segregation types of TC6 can be effectively judged by the methods mentioned above,and the performances of the alloy bar are not influenced by the segregation with the defect areas cut off.It is suggested that the similar defects can be decreased or eliminated by the controls of raw materials for in-got,mixing and electrodes preparation,voltage and current in melting process.