In order to improve quality further of the emergency plans, this paper puts out an assessment method of emergency plan based on atom tasks. Determine the atom tasks by task decomposition to emergency response according to the theory of project management. Assess the efficiency of emergency plan by introducing sufficiency, reachability, operability based on atom tasks, among them using sufficiency to descript the sufficient extent of the atom tasks to the whole emergency response. Descript the opportunity and convenience extent of rescue task completement by introducing the definition of traffic system reachability. Descript the rescue plan operability by introducing 5W1H assessment method. The efficiency of emergency plan is defined as the product of sufficiency, reachability and operability to achieve the whole assessment to the emergency plan. Finally, an application research about an airport emergency plan was given as well. The conclusion shows that defects existed in emergency plan can be found using this method and it can provide support to modify an emergency plan.