The failure of coal mass in the process of coal and gas outburst, which is difficult to calculate by finite element software at present, is studied in this paper. The pre-processing module of ABAQUS is redeveloped by Python language. The coal mesh is re-divided by Python script program, and the zero-thickness cohesive unit is inserted. According to the principle of effective stress and the friction contact of ABAQUS based on Mohr-Coulomb criterion, the simulation of the influence of gas pressure on coal body is realized. The generation and expansion of coal fracture and the outburst process of coal body are simulated by using the cohesive unit. The actual simulation results conform to the experimental law, which proves that the secondary development technology of finite element method can well calculate the failure of coal mass in the process of coal and gas outburst. And it can also provide a reference to the application of Python secondary development in other fields.