According to the characteristics of farm products quality safety incidents, ten samples were processed by the reduction and analysis of attributes using the rough set method, and five indexes were determined. The indexes was toxicity of pollution source, scope of pollution influence, number of death, number of injuries and population density, whose weights were 0.2, 0.2, 0.1, 0.3 and 0.2, respectively, according to the importance analysis of the indexes. Based on these, a grade evaluation model of farm products quality safety accidents was established. An emergency management system of farm products quality safety was designed and implemented by programming the grade evaluation model using WebGIS. Through simulating a particular farm products quality safety accident, the result showed that the system could improve the handling ability of the accident, and realized the visualization of the disposal process. The system can provide consultation for farm products quality safety management. 