Abstract: Light fringe defects were found on products which made of TC4 titanium alloy bar when X-ray test. Chemical compositions, microstructure and mechanical properties of the TC4 titanium alloy bar were analyzed by various physical and chemical methods. The results show that a region of abundant titanium while indigent aluminum and vanadium had been formed in the smelting course because the techniques weren’t controlled well. And gross single α phase which was different from the matrix was produced during the latter thermal processing, which was a typical soft segregation metallurgical defect.