A new instability mechanism in the boundary layer of blunt bodies was studied under reentry conditions by using numerical simulation method.The instability mechanism cannot be addressed by linear instability theory.The recent research shows that

there is a nonlinear instability mechanism associated with local finite amplitude disturbance

which differs from the ordinary instability with respect to the T-Swave and secondly instability.The instability process under the influence of the local disturbance in the boundary layer of blunt bodies was simulated numerically.The physical mechanisms for nonlinear interaction of various disturbance modes were identified in the simulation.