Optical interferometry is an effective way for lubricating film thickness measurement. The dichromatic interferometry can avoid artificial fringe order counting, while operates with a fair resolution and a large film thickness measurement range. However, the traditional dichromatic interferometry depends on strict calibration processes and the observer. In this paper, a dichromatic interference intensity modulation approach is proposed for micro/nano lubricating film thickness measurement, whereby linear superposition of the intensities of the red and the green components is carried out and a modulated signal is obtained to infer the film thickness at its local maximum/minimum. Thereafter the film thickness of other points can be obtained by the interference intensity of the red or green light. To validate this approach,contact gap between a steel ball and a glass disc was measured, and the results were well correlated with the theoretical calculation. A measurement range of 2 μm can be achieved by an optimum selection of the wavelengths of the red and green lights.