Abstract: In order to give full play to the excellent properties of Ti6242S titanium alloy, the high temperature tensile properties and microstructure evolution of Ti6242S alloy with equiaxed and duplex microstructures Ⅰ and Ⅱ three different structures were studied by optical microscope, scanning electron microscope and high temperature tensile test. The results show that in the process of high temperature stretching, the α phase of three different structures have obvious elongation, and the α phase elongation of equiaxed is higher. Equiaxed α phase is beneficial for coordinating plastic deformation, so the plasticity and resistance to uniform plastic deformation of equiaxed microstructure are the best. The presence of both lamellar α phase and acicular α phase will result in interface strengthening, leading to an increase in material strength. And the increase in material strength due to acicular α phase is greater than that due to lamellar α phase, so the strength of duplex microstructure II is the best. In the duplex microstructure II, the intertwined secondary α phase arranged in a basket-like network will promote the formation of tough cavities and reduce the number of tear ridges. Hence, the plasticity and fracture toughness of duplex microstructure II are superior to those of duplex microstructure I.