In order to take advantage of information technology to support social emergency management, it needs to describe emergency plans formally so that they can be correlated with emergency information systems closely. Formal description of emergency plans is the precondition and basis to establish the theoretical framework for emergency plans. Based on the analysis of emergency plans and emergency response processes, this paper proposes a formal description approach for social emergency management system, including the description of organization, the description of emergency resources and the description of emergency processes.