In this paper, we present an optical encryption system which uses the principle of unequal modulus decomposition and polarization vortex optical holography to implement encoding and decoding. Firstly, the original image is decomposed into two complex amplitude images by unequal modulus decomposition method, then their polarization states are changed by vortex beams irradiation, and finally they are encrypted in the photorefractive crystals by polarization multiplexing holographic technology. In decryption, the image can be reconstructed successfully when a series of correct keys are provided. The sensitivity of polarization state and the multiplexing performance of topological charge are also analyzed, proving the method has high security.