The large-diameter solid expandable tubular (SET) with a smaller wall thickness faces the risk of internal pressure burst and external squeeze collapse in repairing damaged casing well. The internal pressure and external squeezing resistance calculation of the tubes using the analytical method require many expansion experiments and postexpansion tensile experiments, resulting in high costs and low efficiency. This paper gives a set of laboratory expansion and postexpansion performance test, which is based on the laboratory experiment and mechanical properties of material expansion. Two materials are studied: 316 L and 20G. Then it analyses the error and causes of the error in the traditional analytical algorithm. Besides, it establishes an accurate finite element (FE) model to study the quantitative influence of expansion ratio and wall thickness on the burst strengths and collapse strengths of the tube. The results show that the toughness and hardening ratio of 316 L is better than 20G at the same expansion ratio. The numerical simulation results of the model can effectively simulate the expansion process and the mechanical properties of SET in good agreement with the laboratory test results. The expansion ratio and wall thickness affect the mechanical properties after expansion. Thus the quantitative laws of the expansion driving force, internal pressure resistance, and external squeezing resistance under different variables are summarized. To ensure the integrity of the reinforced wellbore, the expansion ratio should not exceed 12.7%. The current study lays a theoretical basis and technical support for optimizing SET and preventing downhole accidents.