The inlet boundary is specified by laminar Blasius similarity solution as the basic flow with imposed Tollmien-Schlichting (T-S) waves as the disturbances, the dynamic subgrid-scale model, the high order schemes and a preconditioned algorithm are used in the study of laminar-to-turbulent transition in a spatially developing boundary layer by large eddy simulation（LES）. Simulation result exhibits the linear and nonlinear growth of T-S waves, the formation and evolution of hairpin vortex and multiple vortex rings with four ring-like vortexes, coupled with complex ejection/sweep movements and high/low speed streaks. Finally, the generation and development processes of secondary streamwise vortex are analyzed.