This dissertation first introduces the structure and characteristic of BMP file. Based on the features of adjacent pixels, a steganalysis algorithm for the replacement of LSB is proposed. Scanning and counting the difference of adjacent pixels horizontally and vertically are the first step, and then this thesis judges whether the image contains secret information according to the ratio of odd and even. The development environment is VS2008, and the experiment shows that the algorithm can be simply applied with a small statistics. In addition, the new algorithm has a high detection capability with a large amount of secret information.