For the problem that the oil temperature change caused by external heat flow may affect the lubrication state of friction pair, an external heat source friction lubrication visualization test bench was designed and built. The heat flow was applied to the lubricating oil. The oil film thickness was measured with the visualization device and the cavitation morphology images of oil film were taken while collecting the temperature data. The study found that the speed and oil temperature were the important factors influencing the oil film thickness and cavitation morphology. When the rotation speed increased, the form of cavitation changed from a wide and flat shape to a narrow and long shape and the application of external heat flow can easily destroy the cavitation form and make the oil film disordered and difficult to recognize.