METSIM software is widely used in the process simulation calculation of metallurgy, chemical industry and other industries, especially the material balance and heat balance calculation of process flow, which is an important basis for process package development, project design and plant operation parameter optimization. In recent years, many new magnesite factories has been builded in China. The simulate for 200 000 t/a magnesia calcination process using the METSIM software was introduced in detail, and el the results of mass balance and heat balance were obtained. It can provide a technical support and help for users of METSIM and roasting process.