The combustion process of hydrogen jet lifted flames involves complex processes, such as hydrogen diffusion mixing, flame stability, and local self-ignition. Numerical study of hydrogen lifted flame is of great significance for deep understanding of the fuel diffusion characteristics, flame-turbulence interactions in the combustion process. In this paper, Large Eddy Simulation (LES) and the Flame-let Generated Manifold (FGM) model, combined with detailed reaction mechanisms and unstructured hybrid grid, are employed to conduct numerical simulations of a turbulent lifted H2/N2 jet flame within a vitiating co-flow environment. The effect of jet velocity on flame lift-off characteristics is analyzed. The results indicate that: (1) The predicted temperature field, mixture fraction, and OH distribution agree well with experimental data and related simulations; (2) For different jet velocities (96 m/s, 107 m/s, 117 m/s and 170 m/s), the flame lift-off height increases with rising jet velocity.