In order to accurately measure the lubricating film thickness of mechanical seals,the influence of micro characteristics of impregnated graphite on the accuracy of ultrasonic film thickness measurement was studied.The microstructure of impregnated graphite was characterized by graphitization degree and porosity.Graphite samples with different graphitization degree and porosity were prepared with sintering temperature and particle size as process variables.The acoustic impedance and lubricating film thickness of graphite samples were measured by ultrasonic method.The results show that the acoustic impedance of graphite is increased with the increasing of graphitization degree and decreased with the increasing of porosity,indicating that the influence of graphitization degree and porosity on acoustic impedance of graphite is obvious.The influence of graphitization degree and porosity on lubricating film thickness is not monotonic as the influence on acoustic impedance,the reason is that the internal pores of the sample lead to the measurement error.When the film thickness is 2 μm,the measured values of lubricating film thickness are slightly less than the calibration value,which is caused by that the minimum scale of the calibration device is greater than the roughness of the measured object surface.The acoustic impedance should be tested separately in each test so as to eliminate its influence on the measurement results of film thickness.