Based on block compressed sensing theory and random convolution theory, a new optical image block encryption method based on chaotic convolution is proposed. First, blocks of the same size are created from the plain image. A chaotic phase mask and a chaotic amplitude mask are generated for each block by a cascaded chaotic system, which is then used to convolute the block with the chaotic phase mask, and chaotic subsampling is followed using a chaotic amplitude mask to obtain the encrypted and compressed block image. Finally, all encrypted blocks are restored to the final encrypted image. Note that each block has a different key to increase the security, and fractional Fourier transform is used instead of Fourier transform in the process of chaotic convolution to increase the key space. Simulation is conducted on statistical analysis, noise attack resistance test, cropping attack resistance test, and key sensitivity test. The viability and security of the suggested encryption system are shown by numerical results.