Abstract: The coal mine safety decision-making systems,such as ventilation safety monitoring system,underground water inrush monitoring system,underground coal and gas outburst monitoring system,have been established in many large and medium-sized coal mines of our country.A large amount of original data had been accumulated in these systems.How to transform data into information for scientific decision was a problem need to consider for coal mine safety production.Rough set theory,as a method of quantitative analysis of incomplete and uncertainty knowledge,provided a new method for data mining.In order to solve the problems of reasoning and decision-making in incomplete and imprecise decision tables,a kind of default rule mining model based on reduction extended concept lattice was proposed.Finally,data mining system based on rough set was designed,which was applied in data mining analysis of underground gas emission,and achieved good results.