In mines, tunnel ventilation is monitored using wind speed sensors to measure the stability of the mine ventilation system. However, opening and closing the air door will cause violent fluctuations in the monitoring data of the wind speed sensors. When false alarms are triggered, the staff can diagnose only the mine ventilation system based on their experience. A numerical simulation method is adopted to explore the changes in the flow field during the opening and closing of the air door to address this issue. In addition, a method that is based on the wind speed data of a single sensor is proposed to identify the time and divide the stages of air door opening and closing. The experimental results showed that the proposed method can successfully identify the air door opening and closing time and apply stage division when needed.