Cascaded systems for optical image encryption based on diffractive optical elements are presented. Generally,a cascaded system with n-stages is a 2n-f system constituted with n lens aligning in serial. N diffractive optical elements(DOES)such as phase masks are located in the spatial and the frequency domains of the system so as to decrypt the primary image at the output when the system is illuminated with a corresponding plane wave. These DOEs are designed with the cascaded iterative Fourier transform(CIFT)algorithm. Computer simulations indicate that such algorithms converge very fast,and that the larger the stages number,the faster the convergent speed for the corresponding algorithm. The cascaded systems can perform high quality decryption. Numerical results show that the mean square error between the decrypted image and the primary image can be less than 5×10^－30. Furthermore,the proposed systems can be used as key-sharing implementation in a multiple users system,and higher security is thus achieved.