Abstract: Electric resistance technique is one of the methods used to monitor the lubrication status.The resistance technique has been improved to obtain the time ratio of the metal to metal contact under mixed lubrication regime for a sliding friction system.The method was applied to monitor the transition of lubrication status with O/W emulsion.The influences of concentration and load on the capability of film formation of emulsion have been studied experimentally.The results showed that from the measurement of the time ratio of metal contact,the transition of lubrication status can be monitored and the corresponding critical transition velocity can be detected.By comparison of the experiment result with the theoretical predictive value of the film thickness,it can be concluded that emulsion can form an oil pool in line contact region where the oil concentration is much higher than its bulk nominal value.Therefore emulsion lubrication has some characteristics of oil pool lubrication.