This research conducted microgravity experiments of flame spread over fuel-droplet arrays at a low pressure in order to improve understanding of the flame spread in fuel sprays under high-altitude relight condition of jet engines. The results show that both the flame-spread rate and flame-spread limit distance at the low pressure are greater than those at atmospheric pressure. The pressure effect on the flame-spread rate was discussed considering some elementary processes, such as droplet heating and thermal diffusion. The thermal diffusion speed is inversely proportional to the pressure. The pressure effect on the flame-spread limit distance was discussed considering transient process of high-temperature region around a burning droplet. The maximum radius of the outer edge of the high-temperature region is proportional to -1/3 power of the ambient pressure. Group combustion occurrence was also demonstrated with a percolation model considering the flame-spread limit.