Abstract: Abstract: A 1/5 reduced-scale tunnel model is established using FDS numerical simulation. Through theoretical analysis, the influence of longitudinal ventilation velocity, fire source spacing and heat release rate of fire source on the flame height of double fire sources is studied. The results show that the average flame height and maximum flame height increase with the heat release rate increasing from 60 kW to 120 kW. And, the average flame height and maximum flame height decrease with the increase of longitudinal ventilation velocity (from 0.2 m/s to 0.4 m/s) or the increase of fire source spacing (from 0 m to 0.6 m). Considering the influence of Richardson's number and longitudinal ventilation velocity coefficient, this paper establishes the dimensionless prediction models for the relationship of the merged flame height of double fire sources and fire source spacing.

Key words: Key words: double fire sources, fire source spacing, longitudinal ventilation, flame height