In order to provide effective guidance to the construction and to ensure the safety of workers, numerical simulations were performed on distributions of airflow, temperature fields, oxygen content, and carbon dioxide content during the process of mechanical ventilation using the CFD software. The results demonstrated that, in the course of mechanical ventilation, compared with the pipe trench, the recovery of environmental condition such as temperature and gas volume fraction including oxygen and carbon dioxide were more rapid in the heat chamber. The air flow was mainly along the bottom of the pipe trench and the air velocity at the top of the pipe trench was small because of the internal structure and thermal lift in the pipe trench. For the pipe aforementioned, when the ventilation volume was 6 000, 8 000, 10 000, 12 000, 14 000 m³·h^-1, the minimum ventilation time needed should not be less than45, 32, 22, 15, 10 minutes, respectively. In practical operation, oxygen content at the top of the central part of the trench should be regarded as the key parameter to evaluate the ventilation effects