This paper studies on the triggering mechanism of sliding type rockbursts under weak disturbance. With variation method and by adopting the theoretical model in which a block slides along the interface，induced by weak disturbance under initial stress state. The basic conditions required for sliding type rockbursts were obtained as：(1) The surfaces(referred to the contact surfaces or the fracture surfaces) are in the quasi-steady state with the high initial stress in the tangential direction. (2) The fracture stiffness of the surfaces is larger than the rebound stiffness of the surrounding rock. (3) The impact energy factor which characterizes the movement of the rock mass reaches a critical value，or the relative displacement on the surfaces accumulated to a critical value under the dynamic disturbance. When rockburst occurs，the released energy is far more larger than the energy exerted by the disturbance，the weak disturbance just act as a“trigger”in the occurrence of rockburst，its effect is only to help the rock blocks to overcome the influence of friction on the surfaces. The magnitude of the critical accumulated displacement and the extruding speed of the rock blocks may not depend on the value of the disturbance. The movement(or the extruding speed) of the rock blocks is determined by the relations between the work of the rock pressure and the work of the friction along the surfaces. To prediction the level of sliding type rockburst accurately，the kinetic energy of all the rock blocks at the very time when rockburst occurs should be known.