Abstract: Coal and gas outburst is a complex geo-dynamic disaster induced by a coal seam uncovered by crossdrift, threatens the safety and efficient production of coal mines seriously. For this, Hongshan coal mine was selected as engineering background to simulate mechanical response characteristics of surrounding rock during uncovering No.12 coal seam in a gas bursting hazardous zone with FLAC^3D software. Then the outburst mechanism during uncovering a coal seam by a crossdrift was revealed, and comprehensive outburst prevention technology combining mine gas pre-drainage and improved metal skeleton was put forward. The results showed that the abutment pressure ahead of the working face moved forward dynamically with crossdrift advance, within the range of 6 m from No.12 coal seam, excavation disturbance of surrounding rock in front of the working face was strong, and there was an obvious stress concentration phenomenon in the coal seam, where vertical stress was 1.25-1.58, which had exceeded the coal strength. Meanwhile, surrounding rock deformation increased sharply, roof subsidence displacement was 15~92.22 cm, so that coal elastic deformation energy was accumulated. Certainly, surrounding rock plastic zone also expanded rapidly, and the area on the crossdrift midline vertical section was 10~50 m², until cracks completely penetrated and formed jet channels for crushing coal. So in the process of uncovering No.12 coal seam by a crossdrift, the coal seam was under high concentrated stress and gas pressure, and stored great deal of elastic deformation energy, which easily induced coal and gas outburst. Above all, on the basis of using traditional outburst prevention measures with mine gas pre-drainage, the existing outburst prevention technique of metal skeleton was improved, which had a comprehensive outburst prevention effect, such as gas pre-drainage, coal solidification and advance support. And this was applied to prevent outburst at the site and obtained good effect, provided important reference for outburst prevention when coal seam was uncovered by a crossdrift under the similar conditions.