《傷寒論》是最早全面提出緊脈的形態和治療意義的文獻，文中出現緊脈的條文至少六十七條，是非常重要的脈象之一。若依現代教科書及通行緊脈脈形的定義，是不易把握其脈形特點，也難以和弦脈鑑別，造成臨床應用時不易掌握。本文建立寸口脈「脈象幾何學描述法」之描述座標，以比較各家弦緊兩脈脈形的定義，並歸以《傷寒論》之原文所言緊脈、弦脈之異，推求較合理的緊脈脈形特點。緊脈脈形的特點有二大主軸，一是描述如「纏絲轉索」的動態不穩定狀態，如「絞轉無常位」、「左右彈指」等；二是如「切繩」之穩定靜態形態，如「如切繩狀」、「如紉簟線」等。由《傷寒論》的條文，推斷其緊脈脈形之原意，較符合前者，著重在「無常」；而緊脈和弦脈的鑒別，關鍵則在弦脈為「按之不移」。The “Shang Han Lun” (On Cold Damage) was the first text to mention the tight pulse and its therapeutic significance. The tight pulse is mentioned in 67 lines at least, so it was one of the most important pulses. However, if people take pulse according to the general way described in current textbooks, it is hard for them to fully grasp not only the characteristics of the tight pulse, but also the difference between the tight pulse and the string-like pulse. In this study, we establish the “Geometric description of pulse” to describe the coordinates in the vessel opening so as to compare the different definitions of the tight pulse and the string-like pulse from various issues as well as the original text of the “Shang Han Lun” finally. We hope to build up a more reasonable characteristic of the tight pulse. There are two points of view on nature of the tight pulse. One is a dynamic instability, which is described as “twisting a rope”, “wringing without constant place”, “hitting left or right side of fingers changeably”, etc. The other is a stable state, which is mentioned as “feeling a straight rope”. From the “Shang Han Lun,” we speculate that the original meaning of the tight pulse was an unstable pulse. By comparison, the string-like pulse differs in that it is “stable even while pressing”.