According to statistic data of China in recent years, gas explosion accounted for above 70% in all coal mine accidents. Frequent gas explosion accidents have caused great losses of lives and property. Therefore gas detection and monitoring system is needed to serve as a safety device in coal production. In this paper, an intelligent gas detecting system is designed. This detection instrument adopts SCM AT89S52 as its control hardcore and uses catalytic combustion type gas sensor element MC112 as the sensor for gas (CH4) detecting. The main functions of this system are as follows: monitoring the real-time concentration of CH4 and displaying the concentration value; emitting sound and light alarm signals if the CH4 concentration value is beyond the alarm value inputted by keyboard panel; using serial communication port to transmit data to the host computer above ground. The software debugging and hardware simulating of the system above are also implemented at the same time.