A systematical investigation has been made of the biomechanical mechanism underlying “De Qi” in traditional acupuncture therapy through a biomechanical analysis, followed by a clarification of the physical source and quantitative characterization of the hand mechanical perception of the acupuncturist. Based on biomechanical experimental observations of significant enhancement of tissue displacement and needle force during acupuncture process, a novel mechanical coupling system has thus been established between the elastic needle and surrounding tissues. By constructing a dynamic relationship equation between interface pressure and displacement, a displacement function hypothesis has been proposed for the deformation displacement function of the needle body induced by the force on needle tips, thus deriving the mechanical characterization of the needle practitioners’ tactile feedback, with the model to be validated by using biomechanical experimental data from the Langevin research group. The research results indicate that the mechanical essence of De Qi originates from contraction-induced tissue deformation brought about by needle tip stimulation, which modifies needle curvature and increases insertion forces through tissue-needle coupling; Practitioners’ tactile perception can be quantified as a function of tissue deformation gradient and interface friction coefficient.