To compress and encrypt images synchronously, a joint compression-encryption algorithm by using a hyper-chaos Chen system and a improved zero tree coding was proposed. Based on the improved zero-tree coding, a key stream produced by the hyper-chaotic Chen system was used to modify the context and the decision after bit-plane encoding, then they were fed into a MQ arithmetic coder to compress and produce the corresponding code streams. The code streams were feedbacked into the input end of hyper-chaos Chen system to produce a new secret key related to the plaintext and to realize the joint compression-encryption. Experimental results indicate that the Peak Signal to Noise (PSNR) of proposed algorithm is improved at least 1 dB, and the key space is 256 bit. The encryption time percentages of total time are all less than 45% and the plaintext and secret have higher sensitivity. The proposed algorithm realizes the synchronization of image compression and encryption, and the image reconstruction quality is higher than that of embedded zero wavelet.It is characterized by the high resistance for linear attack and differential attack, a large key space and better safety performance.