Expansion technique is widely used in the field of drilling and blocking, Expansive force is an important technical parameter of expansion technique, also is the basis of expansion tool design. In order to determine the expansive force calculation model, combining with actual stress status of the expandable tube to make basic assumptions, using the elastic mechanics theory to analyze the expandable tube, the expansion force calculation model of the expandable tube was gotten.Making expansion vertebral body which half expansion cone angle was 10 degrees. The expansive force was calculated theoretically by means of the expansive tube, The result show that the theoretical value is roughly identical to the measured value for the expansive force, proving the correctness and rationality of the theoretical calculation model of expansion force. Expansive force calculation model provides theoretical support for the design of the expansion tools.