Abstract: Aiming at the present situation of crosscut uncovering outburst seam relying on experience,from the perspective of rock mechanics,using fast Lagrangian numerical method,reservation thickness of 5,3,2 and 1 m rock pillar were studied when Dongshan coal mine Dong’er crosscut uncovered 3^# outburst seam.Research results visually showed the stress distribution and plastic damage of different rock pillars beared in crosscut tunneling process,which determined a reasonable minimum reservation rock pillar thickness.