High concentrations of methane in tilted coalmine airways can produce methane draft pressure (an additional natural draft pressure due to density difference of methane and air). Methane draft pressure in upward ventilated airways could cause airflow reversion in parallel airways. An experimental system was built to study this reversion phenomenon in this paper. Using this system, 10 tests were carried out to analyze the trend of the airflow velocity and the oxygen concentration in parallel airways. In these experiments, the effects of two main factors, including airway inclination angle and initial air velocity, on reversion phenomenon were discussed. The experimental results show that larger inclination angle and smaller initial air velocity cause a more obvious airflow reversion. There exists a critical initial air velocity to prevent airflow reversion. The relationship between the critical velocity and the airway elevation difference was also studied through numerical simulation and experiments. The results show that the square of the critical velocity is proportional to the airway elevation difference.