Abstract: Expandable theoretical load is the key parameter of drilling technique for Solid Expandable Tubular（SET）. Analyzing method of expandable theoretical load for SET is the theoretical basis for determining the expansion load, designing and optimizing the expansion tool. Combined the structure for SET with expandable process in large plastic deformation, the mechanical model for SET is established. The expandable theoretical load for SET is analyzed. Given the formula of calculating the expansion load for SET is found. It is pointed out that the relationship of expansion load with structure for SET, material properties, structure of expansion tool, and friction coefficient on their contacting surfaces. Through comparison with Finite Element Method（FEM）calculation results and actual engineering case, it proved that the theoretical calculation is simple, the result is accurate, and the relative error is between 3.4% and 5.8%. The result given by the expandable theoretical method for SET is reasonable. The analyzing method is of actual and effective engineering significance for drilling technology for SET.