Abstract: Steganography is the art of covert communication technique by regular-looking media such as images, videos and texts, and the capability of anti-steganalysis is an important factor to measure its security. However, the research of steganography security develops slowly after the introduction of STC (syndrome tellis codes). Most of the existing studies are the completions and supplements of distortion function. In fact, there are two main factors that affect steganography security significantly: one is the embedding-related factor, such as payload or embedding algorithm; the other is the occultation effect of carrier, namely carrier security. In this paper, we study the carrier security by analyzing the relationship between steganography security and the carrier feature based on co-occurrence probability of image residual. We present an evaluation method of security for image carrier based on carrier distance of clustering center. The experimental results show that, by the security evaluation method we propose, the anti-steganalysis capacity of steganography is improved effectively by carrier selection. By the testing of the images under different databases, steganography algorithms, payloads and steganalysis features, the steganography based on our method enjoys a higher carrier security than random carrier selection and the average error rate of detection is improved about 3.8 to 11.8 percentage points.