The materials will show remarkable different characteristics and phenomenon in the nano-scale. It has become unlackable to build and use precise measurement technologies and systems to understand and control the material characteristics. In this paper, a primary surface force apparatus to measure the thickness and refractive index of thin film is developed based on the multiple beam interferometriy. Using the symmetrical three-layer formula from Israelachvili, a software is designed to analyze the Fringe of Equal Chromatic Order (FECO) produced from multiple beam interferometry. Test of the system on the the experimental FECO is shown. The applicability of the system is validated. Further discussion of the factors that affect the formation of FECO is given.