A film thickness measuring rig was developed by coupling an electric capacitance film measuring device to an optical interferometry ball-on-disc apparatus. This measuring rig can realize the film thickness value and its corresponding electrical signals (such as oil film partial voltage value and capacitance value) under identical running conditions based on a specifically designed electric signal acquiring circuit and insulating protection. The variations of optical elastohydrodynamic lubrication（EHL）film thickness and its corresponding electric signal with speed were studied for both oil and grease lubricated contact under pure rolling condition,and the relationship between capacitance and film thickness was analyzed.The results show that the film thickness increases and the oil film partial voltage value and capacitance gradually decrease with the increase of entrainment speed,and the capacitance value decreases with the increase of film thickness.The experimental results preliminarily confirm the capability of the designed system, which can be potentially used to evaluate the lubricating condition of actual contacts in the subsequent studies.