Abstract: A new type of microstructure,named bi-lamellar microstructure of titanium alloy comes out of precipitated small secondary α needles in the β matrix through modification heat treatment.A comparison of microstructure and property of titanium alloy between equaixed,bi-model and lamellar microstructure is made.The results manifest that bi-lamellar microstructure improves the fracture toughness and fatigue crack propagation behavior of TA15 alloys remarkably,increases the length of fatigue crack propagation and brings about large secondary cracks.