Abstract: Using a self-made setup for measuring film thickness, the interference images of the 4010 aviation oil at the contact zone under various conditions (contact pressure, temperature and rolling speed) and lubricating behavior of the 4010 aviation oil were investigated. It was found that the lubricating regime was elastohydrodynamic lubrication at low temperature and high speed, and characterized by a negative relation between central film thickness and contact pressure. While under the conditions of the low temperature, low speed and high-temperature, thin film lubrication regime was observed. In this regime, contact pressure played a less role on the central film thickness. In the EHL regime, the shape of oil film under high contact pressure was flat. The oil film shape was relatively smooth for the thin film lubrication regime. As load increased, the film thickness calculated by Hamrock-Dowson theory was gradually deviated from the measured values at the EHL zone, and the index of rolling speed and load from the theoretical formula should be adjusted. In the thin film lubrication regime, the film thickness was smooth with increasing load.