Abstract: In order to accurately determine the effective drainage radius of slotted drilling, based on the primitive gas content and pressure of coal seam, it combined the two outburst elimination indexes together, which included the pre-pumping rate ＞30% and residual gas content ＜8 m³/t and put forward the new indicator which could be used to measure the effective drainage radius of slotted drilling. When the primitive gas content was less than 11.3 m³/t, it determined the effective drainage radius as the gas pressure has reduced to more than 50% of the primitive gas pressure; While the primitive gas content was more than 11.3 m³/t, it determined the radius as the gas pressure reduced to more than 64/q² of the primitive gas pressure. Through the field experiment in Yangliu Coal Mine, it finally determined that the effective drainage radius of slotted drilling was 5 m. By studying the indicators of gas drainage and the residual gas content, it verified the effectiveness and reliability of the indicators.