Abstract: Necessity of graded power-off was analyzed when gas overran on fully-mechanized mining face. Design scheme of graded power-off module in software of central station of coal mine safety monitoring and control system was introduced as well as graded power-off function of monitoring substation. The graded power-off function can cut off power supply for device with higher power-off priority when volume fraction of gas achieves set value, so as to reduce gas accidents and startup with load of belt conveyer. But the function cannot be realized when wire of gas sensor is cut off and makes adjustment of gas sensor more complicated.