Recently, the deviation of nano-confined flows from classical hydrodynamic theories has been frequently reported. In this work, such a flow is theoretically investigated by means of dissipative particle dynamics (DPD) simulation. The simulation results show that the density and viscosity inhomogeneities near solid/fluid interfaces depends on the slit wettability only. Flow enhancement relative to the Hagen-Poiseuille (H-P) flow occurs together with the flow inhomogeneity. Combining of flow inhomogeneity and the Stokes equation, a theoretical model for flux calculation is established. As the slit being widened, the model can be simplified by gradually eliminating the higher order traces, and be simplified into the model with Navier's slip condition and the well-known H-P relation at last. The theoretical results of flux are in good agreement with the simulations by DPD. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 834-842, 2017