In order to predict the operation status of critical relief facilities(CRFs) postearthquake, and provide decisionmaking references for emergency relief, the quantitative deduction problem of disruption characteristics of CRFs was studied based on the modeling of earthquake disaster evolution mechanism.The GERT method was used to formulate the evolution model of CRFs postearthquake. A numerical method for GERT random network was proposed. By adding the latest information step by step, the activity scenarios and parameters of GERT random network were modified to optimize the deduction results. Finally, a simulation study is carried out for regional medical facilities in disaster area of Dujiangyan in Wenchuan earthquake. The probability, duration and variance of disruptions of medical facilities were predicted. The targeted response measures can be taken based on the deduction results. It can also be used to optimize the decision of the emergency logistics network planning according to disruption parameters of CRFs.