Molecularly thin hydrodynamic film lubrication is the mode of lubrication where the lubricating film is molecularly thin and the lubricating media across the film thickness is molecule instead of the conventional continuum lubricant material. In this lubrication, across the film thickness, the film is non-continuum due to its molecular thickness while the lubricating molecule is discretely distributed and its behavior is thermohydrodynamic random. The lubricating effect of these molecules is the statistical ensemble average of the behavior of these molecules subjected to sliding motion and is determined by the statistical ensemble averaged total flow rate of these molecules through the contact. In this lubrication, the molecular dynamics effect and the non-continuum effect across the film thickness predominantly occur. The molecular dynamics effect includes three components, i.e. viscous, elastic and plastic effects of shear among neighboring molecules, and the non-continuum effect across the film thickness includes two components, i.e. the fluid discontinuity and inhomogeneity effects across the film thickness. In this lubrication, the molecular dynamics effect and the non-continuum effect across the film thickness can be separated from one another and they can be, respectively, taken into account in the analysis of this lubrication. It is proposed that in this lubrication the molecular dynamics effect can be described by the dynamic effect of the equivalent continuum lubricant across the film thickness, and the non-continuum effect across the film thickness can be described by the flow factor due to the combined effects of the fluid discontinuity and inhomogeneity across the film thickness for this lubrication as proposed by Zhang [Zhang, Y. B., Flow factor of non-continuum fluids in one-dimensional contact. Industrial Lubrication and Tribology, 2006, 58, 3.], by the equivalent transformation method. This gives a practical approach to molecularly thin hydrodynamic film lubrication for the theoretical analysis of this lubrication.