Abstract: With dynamic grid technology and DPM technology, control variable method is used to analyze the influence of factors including metro train speed, blocking ratio, number of ventilation shafts on piston wind flow field distribution pattern in the tunnel, and diffusion pattern of pollutants under different shaft numbers. Results show that the distribution situation of piston wind flow field in tunnel and the decay pattern of pollutants in ventilation room is in accordance with test data; the wind volume is proportional to train speed and blocking ratio but has no obvious relationship with the number of ventilation shafts; piston wind speed is directly proportional to train speed and blocking ratio, but has no obvious relationship with the number of ventilation shafts. When pollutants are diffusing, the more ventilation shafts there are, the more serious the pollution in tunnel will be.