The microstructure evolution and tensile properties of the isothermally forged TG6 alloy were studied with different heating time and different deformation degrees of each forging by means of different isothermal forging times and the same total deformation degree. The results indicate that with increasing of isothermal forging times, the content of primary α phases increases, the length of lamellar secondary α phases and the size of sub-β grains decrease at first and then increase, and the thickness of lamellar secondary α phases increases progressively. At room temperature and high temperature the tensile strength of the forging decreases firstly and then increases while the ductility changes on the contrary. For the one-time forging formation with high deformation degree, there are fewer primary α phases in the microstructure caused by temperature rise in the forging; meanwhile more secondary α phases which are long and thin increase the tensile strength of the forging. For the three-time forging formation, more α phases which are fine and equiaxed occur at the sub-β grain boundaries because of different recrystallization degree of every phase in the alloy, leading to the increased ductility of the forging. For five-time forging, the prolonged heating time of the forging results in the aggregation and growth of α phases in the microstructure. When the TG6 alloy is isothermally forged with multi-times formation, there is a critical range for each-forging deformation degree; in the range, partial recrystallization takes place for the forged alloy during air cooling to form fine equiaxed α phases, which restrict the transfer of sub-β grain boundaries, resulting in the small sub-β grain sizes and uneven equiaxed α phase sizes in the microstructure