Expansion technique is widely used in oil and gas drilling field. Expansive force is the key technology parameter of expansion tool reasonable design in expansion technique field.Expansive force calculation model of the expansion pipe was established by stress method. For expansive force analytic expression was relatively complex, introducing hole enlargement factor, by changing the expansion cone angle, expansion vertebral body finite element model and expansion pipe finite element model were established. Adopting finite element analysis method with different friction coefficient, the expansive force of expansion tube was numerically simulated. Results show that the theoretical value and measured value of expansion force are consistent. Through the relationship between the expansion cone angle and hole enlargement factor with different friction coefficient, with the same friction coefficient, hole enlargement factor increases along with the expansion cone angle. When half expansion cone angle was 10°，expansive force was compared between the measured values and the values obtained by the optimized theory model. The results are basically consistent. It is proved that the optimized theory model is reasonable.The introduction of expansion coefficient simplifies the calculation of the expansive force, which provides convenience for the design of the expansion tool.