Abstract: This paper aims to investigate the single coherent structure in the wall regionof a channel fiow by minimal flow unit of direct numerical simulation using psendospectralmethod. The mechanism for the formation and evolution of the coherent structure wasstudied by using the idea of resonant triad of the theory of hydrodynamic stability Theresults compared reasonally well with experirnental observations。Meanwhile,it is foundthat collocation method has higher precision than Chebyshev-τmethod。