The high density inclusions （HDI） in high temperature titanium alloy were studied by means of X-ray test， OM and EDS. The microstructure photos show that the normal microstructure of high temperature titanium alloy is duplex microstructure with α phase content of about 15% after heat treatment， the structure around the inclusion is different from the normal structure. It is widmanstatten structure， high content of β phase， acicular α phase precipitates at grain boundary and in crystal of β phase. The inclusion is obviously different from the matrix， the EDS results shows that the HDI are Ta inclusions. The main reason for the formation of HDI： when batching， high melting point element are mixed in the form of pure element powder and added to the electrode block by manual distribution. It leads to the agglomeration and increases the size of high melting point metal powder. During material melting， the DC arc are can not melt all the powder with large size， the agglomerated powder falls into the molten pool and then enters the solidified ingot to become HDI. It can be improved by changing the distribution mode or selecting multi-component alloy. HDI are not found in the forgings after adding refractory metals by mixing method.