Acupoint is the basis of acupuncture. To elaborate the theory of acupuncture, the structure and function of acupoint should be clarified in advance. By exploring the discussion upon the classification, distribution and structure of acupoint in Huangdi Neijing (Inner Canon of Yellow Emperor), qi zheng lun (on meridian points and extra points), jie jiao lun (on convergence of joints) and guan ji lun (on three-dimensional structure of acupoint) are extracted. Based on whether located on the fixed sites, acupoints are classified into meridian points and extra points, while the meridian points are divided into 4 categories, i.e maishu, gukong, qixue and muxue. The convergence of joints illustrates the principal rule of acupoint distribution. The density of the major and key acupoints is proportional to the size and the complexity of function of joints. Acupoint is recognized as a three-dimensional structure in consideration of its external distribution on the body surface and the substances inside the body, which can be explored and examined. In addition, the relationship between meridian points and extra points, the significance of meridian points in different conditions, and the approaches to acupoint study are deeply discussed and analyzed. The crucial problems and the way for solving them are proposed for the future study to provide the references to the inheritance and innovation of acupuncture.