Abstract: In recent years，blog websites as new network media are more and more paid attention.An algorithm on community detection in blog is presented.Because the bloggers with close hobbies and interests will read and comment on the similar posts，which makes it possible to find out the potential communities which are composed of these bloggers who have the similar interests.This algorithm finds the communities in blog hierarchically and generates the hierarchical structure of the communities.The experiments show that this algorithm is feasible and effective.