A multiple-image encryption method based on two-step phase-shifting interferometry (PSI) and spatial multiplexing of a smooth compressed signal is proposed. In the encoding and encryption process, with the help of four index matrices to store original pixel positions, all the pixels of four secret images are firstly reordered in an ascending order;then, the four reordered images are transformed by five-order Haar wavelet transform and performed sparseness operation. After Aold transform and pixels sampling operation, one combined image can be grouped with the aid of compressive sensing (CS) and spatial multiplexing techniques. Finally, putting the combined image at the input plane of the PSI encryption scheme, only two interferograms ciphertexts can be obtained. During the decoding and decryption, utilizing all the secret key groups and index matrices keys, all the original secret images can be successfully decrypted by a wave-front retrieval algorithm of two-step PSI, spatial de-multiplexing, inverse Aold transform, inverse discrete wavelet transform, and pixels reordering operation.