Abstract: The time-varying structure theory is applied to the researches on the mechanism of rockburst, the energy source of which is analyzed from a new angle. There are self-sustaining bearing structures in the surrounding rock of underground cavern. Furthermore, the concept of self-sustaining time-varying structure is put forward firstly, and the characteristics of the self-sustaining time-varying structures near the underground cavern are analyzed qualitatively. Applying the particle system momentum theorem, the dynamic response of the self-sustaining time-varying structures is calculated. The results indicate that the change of structural mass with time can supply negative damping which can cause dynamic instability and thus induce rockburst. A mechanical model is established to explain how the self-sustaining time-varying structures induce rockburst, if satisfying the two conditions: one is rock dilatancy under tangential stress ?? in the surrounding rock, the other is mass decrease of the self-sustaining time-varying structures. The researches indicate that the mechanism of the rockburst happening in underground engineering can be interpreted well by the time-varying structure theory.