Blog is increasingly becoming an important source of information. Blog community is a kind of a group of bloggers with the same interest and common topics on the Internet. To use blog resources effectively, one important way is to identify blog communities and their members in order to refine the blog circle. In this paper, we first define the blog community and the community center, and then construct the blog community discovery algorithm, and next, we collect and analyze the blog tag data from "sina blogsphere". Through the establishment of "blogger- frequency" matrix, we use the clustering method of data mining to implement the discovery of blog communities.