A new optical encryption technique based on computer-generated hologram of double fractional Fourier transform is presented. In this method, the fractional Fourier transform hologram of several images with different orders are respectively recorded on one plate, which means each image has its own fractional order. In order to reconstruct the encoded images, several fractional Fourier transform systems with certain orders are needed. Because of its particularity of image reconstruction, it is regarded as a new optical security system and can be used in anti-counterfeiting.