The time-varying lubrication regime is a unique feature of the piston ring-cylinder liner tribosystem. This study proposes a new method for comparing oil film thickness with critical values, consisting of characteristic topographic parameters (Rpk, Rk, and Rvk, etc.), to determine the lubrication regime. The lubrication regime could be determined as hydrodynamic lubrication, micro-plasto-elastohydrodynamic lubrication, micro-plastohydrodynamic lubrication, thin film lubrication, boundary lubrication, or mixed lubrication. The influence of thermal effects and oil-feed conditions on the lubrication regime is discussed. It is found that the friction coefficient alone is not entirely suitable for evaluating the lubrication regime of the piston ring-cylinder liner tribosystem. Nevertheless, this new method is capable of determining the lubrication regime under different operation conditions.