In the light of solid mechanics as well as thermal physics, the physical factors causing thermal injury are correlated and a new thermomechanical model is established to quantitatively describe the injury process in living tissues under heat striking. The three-stage mode of thermal injury to living tissue is interpreted. The paper reflects our preliminary effort to further study this clinical phenomenon in point of micro mechanics and thermal science. It is of significance in revealing the mechanisms of subcutaneous bubble formation, development as well as tissue's thermal mechanical disruption.