Effects of high temperature thermomechanical treatment on microstructure and hardness of Ti-1300 alloy under isothermal deformation condition were investigated by means of optical microscope (OM), scanning electron microscopy (SEM), thermal simulation testing machine (Gleeble-3800) and Vickers hardness tester (IMVS-1000JMT2). The results show that high temperature thermomechanical treatment can markedly refine the microstructure and improve the mechanical property of Ti-1300 alloy. Microstructure observation of the hot rolled and hot compressed samples indicates that the tendency of the coarse and elongated grains recovering to equiaxed shape is more obvious, and the microstructure of Ti-1300 alloy after quenching plus aging and solution plus aging treatment is composed of a mixture of primary α phase (αp), secondary α phase (αs) and β phase. The αp phase is mainly distributed in the grain boundary, but the αs phase is mainly in the β matrix after aging treatment. The hardness of the alloy under quenching plus aging is increased due to the growth of αs phase and the remarkable refining of αp phase in width.