Real-time measurement of the lubrication state is one of the critical problems in studying the lubrication state and its transformation characteristics. Based on the experimental results, shrinkage resistance principle and Greenwood's contact theory, a mathematical model for cylinder liner-piston ring that can be used to measure the resistance of film thickness ratio is established. On this foundation, the correspondence between the film thickness ratio and the contact resistance for cylinder liner-piston ring was presented and the technical possibility to characterise the real-time lubrication state was provided. An experimental study for determining the lubrication state of cylinder linerpiston ring based on resistance measurement method was conducted on a reciprocating friction and wear tester to verify the applicability of resistance measurement method in cylinder liner-piston ring friction pair. Results show that the contact resistance method is reliable and practicable to determine the lubrication state of cylinder liner-piston ring friction pair.