Abstract: The unstable rock collapse is a major global geological disaster with the characteristics of mutability, concealment and rapidity. Yet its failure mechanism is still uncertain, thus the research has received more and more attentions from geotechnical engineering circle. The advantages and disadvantages of various methods are compared based on the current linear and nonlinear scientific research results of failure mechanism. By establishing physical and mechanical models, the loads acting on unstable rocks are all concentrated on control fissures, which generalize the mechanical analysis steps. The limitations of quasi-statics theory in solving problems about unstable rocks are also discussed. From the above, the paper makes prospects on the research trends of failure mechanism of unstable rocks and proposes several directions for further research.