Abstract: In order to improve the safety of Structure-Foundation System, the foundation is usually strengthened. The common strengthening approaches are grouting, replacement of concrete (e.g. plug, frame), anchor or prestressing anchor. It is difficult to make technically a comparison among different reinforcing schemes in absence of the index weighing up the reinforcement effect scientifically. Reinforcement Evaluation Theory is thusly developed by means of Least Strain Energy Principle. It points out that the less the strain energy of the system is the better the reinforcing scheme. And the relationship between the energy and some factors, such as elastic modulus, friction coefficient, cohesion, reinforced area etc., has been studied. It shows that strengthening effect increases quickly first and then becomes slow when the factors go up. In addition, the changing tendency of the strain energy during the failure process of Structure-Foundation System is found. The strain energy of system becomes infinite when it is close to failure. The theory is beneficial to determine the reinforce scheme and parameters, which makes reinforcement of the system more effective.