The potential energy curves of some small molecules, H2, N2, O2, F2, HF, CO and NO, in the caged state within C60 cage and in the free state have been calculated by the quantum-chemical method AM1. In this study, the focus is on the cage effect of C60, and the concept of caged state is put forward. The results show that the bond lengths in the caged states are not much different from those in their corresponding free states, but the bond intensities in the caged states are much greater than those in their corresponding free states.