MB1 is a very promising steganographyand few steganalysis methods have been proposed to attackMB1 so far. In this paper, we propose a specific steganalysis method which can effectively break MB1 steganography. We draw some useful propositions based on featurewhich is most sensitive to MB1, and propose an effectiveMB1 steganalysis method. This method outperforms theexisting MB1 steganalysis method in detection reliability,especially in low embedding rate case. What's more, forthe first time, our method also can estimate the embeddingrate of MB1 accurately. Experimental results show thatthe MB1 steganography has been successfully attacked byour method.