Abstract: In view of problems of fuzziness and uncertainty of output signal of gas sensor used in coal mine, the paper proposed a design scheme of gas monitoring system based on BP network and D-S evidence theory. The system uses improved BP algorithm to get basic probability assignment of underground environment and uses D-S evidence theory to fusion information of output of BP network, so as to make judgment and decision of underground gas state. The experiment result showed that the system improves accuracy of monitored gas information and rapidity of decision.