The research of ultrasonic film thickness measurement at present is usually carried out under the condition of fixed probe center frequency (or a single friction pair material),without considering the influence of the change of probe center frequency and friction pair material on the measurable range of film thickness.In order to quantitatively analyze the influence of two factors on the film thickness measurement range,a highprecision experimental device driven by piezoelectric ceramics was designed,and based on the spring model,the water film thickness between different friction pair materials was measured with different center frequency probes.The experimental results show that the measurable value of the film thickness decreases with the increasing of the probe center frequency and impedance value of friction pair.Compared with the theoretical value,the relative error of measuring water film thickness with ultrasonic probe is less than 10%,which verifies the feasibility of the experimental device and method.A method was proposed to determine the effective bandwidth of the probe according to the friction pair material and the expected measurement film thickness range and was verified by experiments,which can provide a reference for the selection of ultrasonic probes when measuring different film thicknesses in engineering practice.