Acupuncture, which is a branch of traditional Chinese medicine, is a kind of physical therapy. It is a very accurate, fast acting, simple and safe medical manipulation. Among ancient Chinese medical works, Huang-ti-nei-ching is the oldest. Later, the Chia-i-ching written in the Chin dyansty gave the depths of needling for the individual acupoints. Subsequenctly, the Chen-chiu-ta-cheng reviewed all writings on acupuncture. Recently, both Taiwan and mainland China have published many specialized books that integrate acupuncture with modern anatomy, physiology and histology, and which define more clearly and accurately needling depths of needling for the various acupoints. The aim of the present investigation is to understand if there is any difference in the needling depth for each acupoint that may have occurred with the passage of a history of more than two thousand years. We looked up records on depths of acupoints of the hand tai yang small intestine meridian from literature of the various generations from the Chin, Ming, and Ching dynasties down to modern times in order to find out the answer. Using the traditional tung-shen-tsun (body equivalent scale) as a common measurement unit for comparison of the different values of needling depth for the same acupoint, we plotted graphs with Microsoft's Excel program to show the differences from which we have found that depths given in the Chung-hsi-chen-chiu-ke-hsueh (Chinese and Western Acupuncture Science) and Hsin-chen-chiu-hsueh (New Acupuncture) are deeper than in other works.