The mechanical anisotropy of high temperature titanium alloy Ti65 plate under the conditions of original state, aging state and high temperature state was studied by unidirectional tension. Optical microscopy (OM), electron backscattering diffraction (EBSD) and scanning electron microscopy (SEM) were used to observe the microstructure of each state. The results show that original Ti65 sheet has highest strength in RD and lowest strength in the 45° direction, which is due to the elongated α phase and strong crystallography texture: (0001) ∥RD-TD plane and <10-10>∥RD. After aging at 790℃, Ti65 sheet has highest strength in TD because of the coarsing of α phase and weakening of fiber structure. At 790℃, the thermal tensile strength decreases greatly, and anisotropy changes obviously. The TD strength is remarkably higher than other two directions, primarily because the critical resolved shear stress of each slip system in α phase decreases greatly with the increase of temperature and the decline of different slip systems is different. In addition, there is stronger recovery and recrystallization at high temperature. The fracture mechanism of Ti65 at room temperature is ductile, and the fracture mechanism at 790℃ is interconnected by dispersed micropores.