By using the method of direct numerical simulation, the coherent structures in the wall region of a turbulent boundary layer with either steady or changing pressure gradients were studied. Initial values of the coherent structures in the wall region were obtained on the basis of the idea of resonant triad in the theory of hydrodynamic stability. It was found that the results of DNS match with those of experiments very well in many aspects. Pressure gradients have much more effect on choosing preliminary waves than on evaluating of the coherent structures. The longitudinal vortices probably result from the streak lines.