It is generally believed that the "β fleck" in TB6 titanium alloy will reduce the mechanical properties of the component, and the main cause of the β fleck in TB6 alloy is Fe element segregation. In this paper, the differences of microstructure, chemical composition and hardness between β fleck and normal area were analyzed by OM, SEM, EDS and EPMA, and the effect of β fleck on the tensile deformation behavior of TB6 alloy was studied. The results show that the content of primary α phase in β fleck is less than 5%, and the β grain size is coarse up to 0.58mm, which is more than 60 times of normal grain size. The vickers hardness of β fleck was slightly higher than that of normal area. The results of composition analysis showed that there was no significant difference of V and Fe between in β fleck and normal area, but there were fluctuations and uneven distribution of Fe content within the microregions . Fe content dispersion in β fleck was higher than that in normal area. The difference of V and Fe elements in microregions is the main reason for the difference in the phase transition temperature of TB6 alloy during subsequent heating and deformation. The preconverted β grains grow rapidly due to the lack of grain boundary α phase pinning. In the process of in situ SEM tensile, the crack starts at the grain boundary of the coarse β grain, grain boundary and intra-crystal slip is the main deformation mode of β fleck structure. The fracture mode of TB6 alloy contains of β fleck is intergranular and transgranular mixed fracture mode.