In order to improve the security of multi-image encryption and solve the problem of large amount of data in multi-image encryption system, the encryption method based on block compressed sensing and improved magic square transform was adopted. During the encryption process, the sensitivity of chaotic sequence to initial value was fully utilized and the periodicity of encryption algorithm based on traditional magic square transformation was solved. Combining the block compression sensing method, the amount of data in the encryption system was reduced. Four 256×256 gray-scale images were encrypted and tested. The results show that the encryption time of the system is only 0.98s. The quality of the reconstructed image is high. The correlation coefficients were higher than 0.99. Peak signal-to-noise ratio (PSNR) values are greater than 35dB. This algorithm reduces the amount of data in the encryption system and further improves the security of the system. The algorithm is easy to implement and can complete multi-image encryption efficiently and safely.