To overcome the low efficiency in artificial estimation of the film thickness in an optical sliderondisc lubricating film tester,a robust algorithm was proposed to recognize interference intensity variation and its order change,which enables automatic measurement of film thickness.Theoretical and experimental results show that the multibeam interference principle can be applied to the film thickness measurement in the sliderondisc contact,and the interference intensity profile can be divided into regions I and II within one film thickness period.Freeman chain code and simple moving average filter technique were used to smooth the data.A normalization algorithm based on threshold value was proposed for determining in which region the data are,and the interference order can be obtained accurately.A template matching method was used to infer the shape of the start and the end areas.This approach was applied to process measured data in the experiments,and results were in good agreement with the oil film thickness calculated by the old method.