Abstract：The forming mechanism of geological hazards triggered by external disturbance such as earthquakes，rainstorms and engineering activities，etc.，is analyzed deeply by means of nonlinear science. And the forming mechanism is summarized to two effects：effect of micro-disturbance under critical condition and effect of macro-disturbance under near critical condition. A lot of phenomena about geological hazards can be explained perfectly using the two effects. The results of studies show that when the evolution of geological bodies is to the critical state，the micro-disturbance can trigger geological hazards，while if the evolution of geological bodies is near the critical state，the macro-disturbance can trigger geological hazards in advance.
