When a transparent plane parallel plate is coated by a transparent film, the interference pattern of light in the plate is changed. This change has been exploited to measure the growth rate, the optical thickness, and the refractive index of the film. Using CCD, this technique enables to measure these quantities at each point on the plate, therefore, it provides a good mean for studying the homogeneity of overgrowth distribution and the change of refractive index in growth process. By this technique a quarter-wave thickness can be monitored very precisely, and also film thickness of many wavelengths can be measured. The technique easily can be applied, there is no need for calibration, and precision is quite good.