It is known that chromatin three-dimensional (3D) structure plays important roles in nucleus.Recently,the extensive works from chromosome conformation capture (3C) derived techniques,such as Hi-C,have further revealed that topological domain,or topologically associating domain (TAD),is a pervasive element in organizing chromatin 3D structure across species.However,previous works mainly treated domain as a whole unit,so the internal structure of TAD is not well studied.