An optical method for directly measuring the thickness of a thin film has been proposed by means of multi-wave laser interference (Semiconductor Diode Laser) at many incident angles, and confirmed experimentally by means of equipment made on an experimental basis. Two methods are available: one can be used when an index of refraction of the film, a wavelength λ, and two successive angles of incidence at which the sinusoidal light intensity has minimum values, are known (Method I), and another can be used without an index of film refraction when three successive angles of incidence and a wavelength are known (Method II). A two thin film samples were used in the experimental work. They were: Polyester transparent film and Silicon wafer coated by Aluminum layer. For Polyester film the smallest measurable thickness is 0.93 μm for method I, and 1.63 μm for method II. The largest measurable thickness is about 65 μm for both methods. For Aluminum layer the smallest measurable thickness is 0.36 μm for method I, and 2.9 μm for method II. The largest measurable thickness is about 84.2 μm for both methods. Theoretical values of the reflectivity as a function of incidence angles for the two thin films samples were get by using MATLAB7 software program to use in the compression with the experimental results. A thin film software analysis (TFCompanion) was applied on a film stack sample (ZnS and MgF2) to study the effect of spectral reflectance and transmission for many wavelengths, incident angles, and various values of physical thickness, and this analysis was applied to enhance this work.