The theoretical model of symmetrical and asymmetrical coherent structures in a near-wall turbulent boundary layer is established through study into the impulsive disturbance on the wall in this paper.Theoretical mechanism and evolution process of the coherent structures formation are studied by Direct Numerical Simulation (DNS).The numerical result reveals that asymmetrical coherent structures are more likely to grow than symmetrical coherent structures,due to the larger span wise velocity induced by asymmetrical coherent structures in the near-wall area.And the dynamical mechanics of the coherent structures in the near-wall turbulent boundary layer vary with different distributions of initial structure.The proposed model relatively represents the real condition of fluid motion,and will help to improve the understanding of the dynamical mechanics of single coherent structure formation in the near-wall turbulent boundary layer.