Abstract: In order to plan pre-draining period of coal gas reasonably,based on gas seepage theory,the determination method of rational pre-drainage period is discussed.The gas flow equation of coal body which around the drainage holes is built up,and the solver with MATLAB is work out.The solver is applied on the workface of No.8 coal seam in Duerping mine.The results show that with the same pre-drainage period,the smaller drills space is,the greater gas pre-draining rate is.