An automatic photometric ellipsometer with a rotating analyser was constructed on a coating plant for in-situ inhomogeneity measurement of thin film during deposition. The information on inhomogeneity is obtained with the aid of the trace of the elliptical parameters Δ and Ψ versus film thickness. The experimental result suggested that transition layers of lower index may exist on either side of ZnS and ZnSe film while central parts between the transition layers are essentially homogeneous.