In TCM theory, acupoint is not a fixed point but a portal with dynamic characteristics where the channel qi enters and flows out. The dynamic characteristics have been verified primarily by detecting the tenderness reaction on Diji (SP 8) in primary dysmenorrhea patients. In this study, finger pressing and algometer were applied in Diji (SP 8) area of participants in menstrual period and nonmenstrual period, respectively, to detect the tenderness occurrence rate, the VAS score of the tenderest point, the tenderness threshold of the tenderest point, and the location of the tenderest point. The result suggests that the acupoint may not be a fixed location but a point in a dynamic state within a certain range in time and space varying with different physiological and pathological status.