The theory, methods and ideas of "experiment of progated sensation along meridians (PSM)" were examined in the article through retrieval of ancient medical books, excavating the theory of meridians, the qi of meridians, ying (nutrient) qi, wei (defensive) qi and the related acupuncture techniques. The result shows that PSM is not the reaction of the meridian qi, but the reflection of wei (defensive) qi. Therefore, whether the experiment of PSM revealed with the phenomenon of meridian and all hypothesis based on it or not are still remained as a question. However, although PSM is considered to be related with the wei (defensive) qi, it can not be concluded that the experiment of PSM revealed the function of the wei (defensive) qi.