Introducing a hardening layer on the component surfaces is a widely used approach to prolong their service life. In cases where the hardening layer exhibits gradient properties in hardness, the lubrication response may be significantly influenced, largely due to the complex elasto-plastic behavior that arises from the gradient. In this study, a systematic set of plasto-elastohydrodynamic lubrication analyzes were conducted to study the evolution of lubricant film with respect to various gradient hardening layers. To validate the developed model, the degenerated results were compared with those from finite element simulations and relevant literature. The effects of layer thickness, hardness level, and hardening behavior on central film thickness were discussed, and the observations were explained by the variations in elasto-plastic deformation and the resulting contact pressure. The findings offer a direction for optimizing the lubrication response by tailoring the thickness, hardness level, and hardening property of hardening layers.