The principle of the interaction between surrounding rock and support plays an important role in the support design and safety evaluation of underground engineering. The convergent constraint method based on this theory is also an international popular support design method. However, the principle of interaction does not consider the characteristics of underground engineering that excavation is first and supporting is second, but assumes that excavation and supporting are completed at the same instant. At present, scholars have proved that tunnel excavation and supporting meet the loading and unloading conditions defined by plastic mechanics, which shows that plastic deformations occur in excavation process, while elastic deformations occur in supporting process. The theoretical analysis of a circular tunnel satisfying the Mohr-Coulomb yield criterion shows that the displacement increment of the surrounding rock caused by the supporting is proportional to the supporting stress, while the traditional characteristic curve of the surrounding rock does not conform to the law. From the finite difference numerical calculation software FLAC to simulate the excavation and supporting of a circular tunnel. It shows that the displacement increment of the surrounding rock is proportional to the supporting stress in supporting process. This indicates an elastic law. Therefore, the characteristic curve of surrounding rock in the previously widely used principle of surrounding rock-support interaction is not correct in terms of plastic mechanics theory.