The paper aims to propose a multi-image synchronous encryption algorithm based on phase truncation in cylindrical diffraction domain and discrete cosine transform to realize the fast-synchronous encryption of multi-images and enhance the anti-cracking ability of the encryption system. Firstly, the compress transform (CS) was introduced to compress input plaintext. The compressed plaintext was decomposed based on discrete cosine transform (discrete cosine transform) to obtain the corresponding DCT coefficients. And these coefficients were combined into matrices. Iterative complex function was constructed to fuse the coefficient matrix corresponding to each compressed plaintext into a complex matrix. And a combined image was formed by reversible DCT method. The modulation mask was constructed by combining Hilbert transform with waveband plate phase model. Finally, the ciphertext and private key of combined images were obtained by introducing the phase truncation mechanism in cylindrical diffraction domain and modulation mask. The experimental data showed that compared with existing multi-image synchronous encryption, the proposed algorithm had higher encryption security. Its entropy of ciphertext and correlation coefficients between adjacent pixels were 7.998 and 0.0012, respectively. It also has stronger key sensitivity. This encryption algorithm can resist external attacks in the network, which has certain reference value in the field of anti-counterfeiting of image information.