Abstract: A medical TC4 ELI titanium alloy sheet was found to have a penetrating bright band defect during macroetch examination.Through metallographic examination,scanning electron microscope analysis,energy spectrum analysis and hardness test,the type and causes of the defect were analyzed.The results show that the defect was Ti-rich and interstitial element segregation defect,which was caused by the uneven particle size of titanium sponge and the uneven distribution of master alloy mixtures in the production process of titanium alloy ingot.It was recommended to reduce or eliminate the defect by controlling raw materials and smelting process.