A copy protection method includes the steps of providing an optical storage device having a substrate layer and a data structure layer coated on the substrate layer and containing a set of raw data codes; forming on the data structure layer at least one polarizing layer capable of causing a change in a light beam; and forming on the polarizing layer a scratch protection layer. The polarizing layer is located between the data structure layer and an optical reading device to influence a light beam irradiated thereon by the optical reading device, so that the set of raw data codes being optically accessed is conditionally converted into a different set of physical data codes. By providing the polarizing layer on the optical storage device to change the data codes that can be obtained by the optical reading device, it is able to stop illegal copying of the optical storage device.