Abstract: The influence of different solution and aging conditions on the microstructure, impact toughness, and crack initiation and propagation mechanisms of the novel α + β titanium alloy Ti6422 was systematically investigated. By adjusting the furnace cooling time after solution treatment and the aging temperature, Ti6422 alloy samples were developed with a multi-level lamellar microstructure, including microscale α colonies and α_p lamellae, as well as nanoscale α_s phases. Extending the furnace cooling time after solution treatment at 920°C for 1 h from 240 to 540 min, followed by aging at 600°C for 6 h, increased the α_p lamella content, reduced the α_s phase content, expanded the α colonies and α_p lamellae size, and improved the impact toughness from 22.7 to 53.8 J/cm². Additionally, under the same solution treatment, raising the aging temperature from 500 to 700°C resulted in a decrease in the α_s phase content and a growth in the thickness of the α_p lamella and α_s phase. The impact toughness increased significantly with these changes. Samples with high α_p lamellae content or large α_s phase size exhibited high crack initiation and propagation energies. Impact deformation caused severe kinking of the α_p lamellae in crack initiation and propagation areas, leading to a uniform and high-density kernel average misorientation (KAM) distribution, enhancing plastic deformation coordination and uniformity. Moreover, the multidirectional arrangement of coarser α colonies and α_p lamellae continuously deflect the crack propagation direction, inhibiting crack propagation.