Abstract: Ti80 alloy is a corrosion-resistant weldable near-α titanium alloy independently developed by China. Marine equipment puts forward higher requirements for the strength, plasticity and impact toughness of Ti80 alloy. In this study, three typical microstructures of exquiaxial, duplex, and widmanstatten structures of Ti80 alloy are obtained by adjusting the annealing temperature, and the mechanical properties are tested. The evolution law and strengthening and toughening mechanism of Ti80 alloy are clarified by SEM and EBSD techniques. The results show that the excellent compatible deformation capability of the equiaxed α phase makes the equiaxed and bimorph structures have excellent plasticity, and that the poor compatible deformation capability of the interlaced α clusters leads to the poor plasticity of the Vermanchii structure. The impact energy absorbed by the Westmanstatten structure is the highest. The difference of the impact properties of the three structures is mainly due to the difference of crack propagation work. The α phase of the duplex structure has excellent plastic deformation ability, and the lamellar α phase has good crack deflection action and certain plastic deformation ability. The relatively tortuous crack propagation path and good plastic deformation along the crack path make the duplex structure have the best strength, plasticity, and impact toughness.