Coverless steganography can hide the secret information without modifying the carrier by extracting the features of the carrier and mapping with the information sequence. Therefore， it has strong ability of anti-steganalysis， but the existing algorithms are still limited in hiding capacity， and most of them need to construct a library with large number of images. In this paper， a coverless steganography algorithm based on image block chaos scrambling and discrete wavelet transform （DWT） is proposed. The parameters of chaos transform are extracted from secret key， and the cover image is scrambled to generate multiple new images. Then， block DWT transform is used to generate the corresponding hash sequence according to the relationship between the low-frequency DWT coefficients of adjacent image blocks， and corresponding index library is constructed. The cover image and secret key are sent to the receiver to realize the transmission of secret information. Experimental results show that compared with the existing algorithms， the proposed algorithm not only has a great improvement on the capacity and success rate of information hiding， but also has strong robustness. At the same time， the algorithm has a simple architecture and small transmission load， which shows strong practical value for application.