Aiming at the need of the safe operation of mechanical structure, an effective method to measure the thickness of lubrication film using ultrasonicre sonant technique is developed. A model of three layers is constructed to simulate the propagation of normal incidence ultrasound. By the analysis of reflection coefficient of lubrication film with different thicknesses, the resonant frequency of reflection coefficient is used to characterize the thickness of lubrication film. After the calibration of experimental system, the experiment of lubrication film thickness measurement is conducted using ultrasonic resonant method. It is shown that the measurement results agree well with that of the actual condition. Meanwhile, the influences of acoustic properties of three layers on the reflection coefficient and measurement of thickness are studied. The results show that the thickness of lubrication film can be characterized by the resonant frequency of reflection coefficient. The error of measurement remains less than 5% on the basis of the calibration of experimental system. It has little or no effect on the measurement when both sides of lubrication film are changed. However, the measureme nt system needs to be calibrated before changing the material of lubrication film.