In this paper, we use molecular dynamics (MD) simulations to study the mean free path distribution of nonequilibrium gases in micronanochannel and to model the Knudsen (Kn) layer effect. It is found that the mean free path is significantly reduced near the wall and rather insensitive to flow types (Poiseuille or Couette). The Cercignani relation between the mean free path and the viscosity is adopted to capture the velocity behavior of the special zone in the framework of the extended Navier-Stokes (NS) equations. MD simulations of flows are carried out at different Kn numbers. Results are then compared with the theoretical model.