Abstract: The method of emergency planning for large nuclear reactors can not be applied to small nuclear reactors directly. The division of the emergency planning zone should give full consideration to the expected dose and the dose that may be affected by the public, and to determine the scope of the emergency plan by comparing the obtained dose data with the prescribed intervention level. Take the plume emergency planning zone outside which the expected dose not more than 10 m Sv as example, calculate the release of the source item level requirements under the constraints of the emergency planning zone by using MACCS, and give a detailed description of emergency plan zone of division and the calculation process.