In order to study the occurrence mechanismin of penetration stability failure of coal containing gas,it was supposed that the outburst be a process of coal mass as a form sublayerpushing forward. Based on the totall stress method,a simplified calculation formula of the critical improved gas pressure gradientwas given. According to the formula,the critical improved gas pressure gradient is directly proportional to shearing strength,and is inversely proportional to the uncovering coal circular section radius...