Abstract: A new image parallel encryption strategy is proposed based on the improved hyperchaotic sequences and ciphertext diffusion in crisscross pattern. Firstly, the hyperchaotic sequences are modified to generate chaotic key stream that is more suitable for image encryption. Secondly, the final key stream is generated by correlating the chaotic key stream and plaintext which result in both key sensitivity and plaintext sensitivity. The plain-image is firstly divided into two sub-images, then sub-images are encrypted simultaneously in a parallel manner with two rounds. The technology of ciphertext diffusion in crisscross pattern is introduced. Performance test and security analysis are performed using key space analysis and algorithm efficiency test, the pixels distribution character, correlation coefficients, the ability to resist differential attack and key sensitivity test. Results suggest that the proposed image encryption scheme is secure and efficient, with high potential to be adopted for the secure image communication applications.