The rock strength will decrease under a certain stress

which can lead to different performances in engineering such as the abrupt destroying by strength weakening

long-term strength and so on. So the research on time dependence of rock strength is very important to construction safety and long-term stability of rockmass engineering. Based on the analysis of a large number of test results

evolution characteristics of rock strength and their mechanisms are summarized

and it is can be found that strength weakening of rock is related to the inherent strength of rock

the stress state (yield approach index) and the performing duration of stress. Therefore

time-dependent theoretical model of rock strength is proposed by properly theoretically characterizing the evolutions of cohesion and frictional angle of rock. Simulations to some sets of test data show that the proposed model can perfectly and quantitatively describe the evolution of weakening process of rock strength; moreover

the model is of clear physical concept. The effort of this paper gives a new method to study the time-dependence of rock strength.