Abstract: A laser generation and modified optical difference detection method of SAW for studying the characters of thin films deposited on substrates is introduced. Based on the acoustical dispersion relations acquired from the experiments and the parameters of the substrates, the elastic constants, density and thickness of the film can be simulated by using the theory of elastic wave propagation in thin layers. Three films, Fe, Au and Si films, deposited on glass plates have been studied and the related parameters have been evaluated. In order to analyze the simulated results, the scanning electronic microscope (SEM) and X-ray diffraction (XRD) analyses, the results of the films have also been obtained. Comparing with the published values and combining with the SEM and XRD analyses, show that the method is a validity technology for evaluating the mechanical and elastic characters of thin film materials.