Abstract: The deformation and failure of rock mass structure is an asymptotic process, which cannot be described by conventional strength design and limit analysis. After reviewing the methods of failure control and deformation control of rock mass structure, we proposed a cracking control method, which should be the final control of the deformation and failure of rock mass structure. We analysed the difficulties of cracking simulation of rock mass structure, and expounded the theoretical basses for describing it by unbalanced force. We analysed the correlations between cracking and unbalanced force by three numerical cases: uniaxial compression test, excavation and unloading of slope and arch dam cracking test. It is proposed that the irreversible valley width reduction caused by impounding is also the result of unbalanced force: the pore water pressure shrinks the yield surface, making that the original stress state of rock mass exceeds the yield surface, resulting in unbalanced force and irreversible plastic deformation. Unbalanced force describes the distance from the unbalanced state to the balanced state of the rock mass structure, and the general trend of the evolution of the unbalanced rock mass structure obeys the principle of minimum plastic complementary energy. Unbalanced force can not only be used as the criterion of deformation and failure of rock mass structure, but also provide corresponding reinforcement measurements, which is of great engineering significance.