The coal seam C5 in entrance section of Yujingshan Tunnel on ChengduGuiyang Highspeed Railway is determined to be risky because of gas outburst. In order to ensure the construction safety and avoid gas accidents, the gas drainage technology of penetrating meshy boreholes is adopted. By comparison among several schemes, the drilling field is set in left side of parallel heading, gas drainage of parallel heading and main tunnel is carried out at the same time and the control range, borehole span and endhole span of gas drainage are decided. The gas outburst elimination includes three parts, i.e. regional outburst prevention, local outburst prevention and rock outburst prevention. The value of the gas desorption index K1 and gas concentration are used to testify the effect of gas outburst elimination. The realtime monitoring results about gas concentration and air velocity based on KJ83N online system show that by using deadend forced ventilation with two fans, the airconditioning requirements can be met. The systematic technology of gas drainage used in Yujingshan Tunnel is successful; and the effect of gas outburst elimination is obvious, so as to guarantee the construction safety of tunnel crossing coal seam.