Introduction: The purpose of this study is to provide anatomical information of BL40 in- cluding applicable needling depth, bloodletting methods and related physiological effect. Methods: The contents about BL40 were extracted from literature. Then we investigated the clinical effect, needling feature (depth/angle/stimulation method) and the bloodlet- ting methods of BL40, searching online databases like ‘RISS’, ‘Oasis’, ‘DBPIA’, ’Naver Aca- demic information’, ‘National Research institute of Korea’, ‘Pubmed’, ‘Google scholar’ and ‘CNKI’ from 1990 to 2023. Results: According to the classic test, the needling depth of BL40 is 9.35-33.15 mm, that of previous research is 9.4 mm-23.4 mm. When acupuncture is applied at that level, stim- ulatable anatomical structures were deep popliteal fascia and tibial nerve. Conclusion: The remarkable effect of BL40 is originated from stimulation of deep popli- teal fascia and tibial nerve. It is necessary for BL40 to be stimulated as 15.5 mm depth.