Abstract: In order to find a high speed secure encryption of image, an encryption based on bit planes division for optoelectronic devices is studied. The research focuses on the security and the ability against the invader of the encryption. The simulation results show that after encrypted, the information in the image is reduced, and the change of average gray-level of encryptedimage is larger. The results demonstrate the gray-level transform cancels the correlation among pixels of primary image, and the pixel distributes randomly, which makes invader hard to analyze correlation and find outline of the original image. Hence, this encryption has a high security, and the average gray-level of encrypted image is more suitable than the change of average gray-level.