Structural connotation of fabric is analyzed from the definition, formation and design of fabric. And structural classification of fabric by systematic method is also provided. Fabric structure is inevitably classified into four aspects, i.e., geometrical structure, compact structure, pore structure and surface structure. The intension system model is established from the structural hiberarchy, geometry and aggregation of composed elements in fabric. And the complexity, changeability and polyaphaism of fabric structure are interpreted from its connotation. It is complexity, variability and polymorphism of fabric structure that lead to the difficult determination of fabric structure. So it is difficult to form fabric design and objective products, which also further stress the importance to study fabric structure by systematic method. All these conclusions can lay a solid foundation for extraction of textile science.