A method of evaluating the quality of a thin film layer may include: forming the thin film layer on a substrate; applying a stress to the thin film layer; and evaluating the quality of the thin film layer. A device for evaluating the quality of the thin film layer may include a stress chamber for applying a stress to the thin film layer and a refractive index measuring unit for evaluating the quality of the thin film layer based on a rate of change of a refractive index.