Summary: Direct numerical solution of a temporal compressible mixing layer has been performed through the mixing layer transition at convective Mach number 0.4 with massively parallel computer. Finite volume method has been used to solve the full time-dependent, compressible Navier-Stokes equations without turbulence models. Numerical simulation initialized by the most amplified linear instability waves is then presented. \(192^3\) mesh size is used to describe full scales. Roll-up and pairing process have developed and have been described, showing the highly two-dimensional feature of the mixing layer. The influence of the phase between the two- and three-dimensional initially perturbed waves has been revealed.