SummaryIn this article, a small‐scale experiment (1:10) is used to study the flame morphology of the dual fire sources in the tunnel under longitudinal ventilation. The experimental results show that: (1) The flame height increases with the heat release rate of the fire source. When there is no wind, the flame height will increase as the fire source spacing increases. Under the effect of longitudinal ventilation, the flame height decreases first and then increases as the fire source spacing increases. (2) The flame inclination angle increases as the heat release rate of the fire source increases. When there is no wind, the flame inclination angle decreases with the increase of the fire source spacing. Under the effect of longitudinal ventilation, as the fire source spacing increases, the flame inclination angle decreases first and then increases, which is consistent with the variation law of the flame height with the fire source spacing. For the experimental conditions of smaller heat release rate of fire source and larger fire source spacing, the flame merged phenomenon gradually decreases.