Abstract: An initial physical model on the symmetrical and unsymmetrical coherent structure in the near wall region of turbulent boundary layer generated by a certain local impulse disturbance is proposed. Direct numerical simulation is used to analyze the formation mechanism and the development law of the symmetrical and unsymmetrical coherent structure in the near wall region of turbulent boundary layer, particularly the evolution characteristics of symmetrical and unsymmetrical coherent structure, so as to identify which structure is more likely to be stimulated and generate, and the reason of rapid increase of excitation. The thorough research enables better understanding of the formation mechanism and evolution process of turbulence, and is also important on the aspects of energy and momentum transports of turbulance.