Ancient literatures on traditional Chinese medicine were retrieved, and theory of Biao (Branch) and Ben (Root) of meridians was studied from the aspect of acupuncture based on tracing of Weiqi (defensive qi). It was found that Biao and Ben were related with the gathering and dispersing of Weiqi (defensive qi) in 12 regular meridians. Therefore, observation of Weiqi (defensive qi) and tracing its running course is required before the application of acupuncture. Disease may cause migration of Weiqi (defensive qi) between Biao and Ben of meridians. Thus, points selection from Biao of meridians, Ben of meridians or both Biao and Ben can be adopted. Primary disease and secondary disease are held as the primary consideration for point selection from Biao or Ben. The idea can also be applied in treatment of complicated syndromes to clarify and simplify the situation. And during the treating process, physicians should proceed from Biao to Ben so as to conduct the anti-pathogenic qi to play its role in disease cure and health maintenance.