This paper offers an overview of numerical simulation with the aim of improving the knowledge and reference of coal mine gas distribution rule, and providing a case study of the optimization of ventilation system and environment protection. The numerical simulation experiments based on U shape ventilation system and U+L shape ventilation system are performed respectively. The results indicate that U+L shape ventilation system is more effective than its counterpart in terms of accelerating the gas flow, balancing the air pressure, and lowering the gas content of the upper corner. Besides, the field verification shows that the average gas content of tail airway, upper corner and air outlet have decreased from 1.86%, 0.79% and 0.58% (U shape ventilation system) to 1.68%, 0.75% and 0.55% (U+L shape ventilation system) respectively, and the average gas drainage rate of special drilling tunnel has increased from 43.4 m3·min-1 (U shape ventilation system) to approximately 51.8 m3·min-1 (U+L shape ventilation system).