An experimental and numerical analysis were conducted to investigate the transient temperature distribution and flame propagation characteristics over an inline polystyrene spheres under microgravity. From the experimental, a self-ignition temperature of polystyrene bead was 872 K under gravity. Flame spread rates were 4.7-5.1 mm/s with ambient gas N$_2$and 2.3-2.5 mm/s with ambient gas CO$_2$, respectively. Flame radius diameters were 17 mm with ambient gas N$_2$and 9.6 mm with ambient gas CO$_2$, respectively. These results suggest that the flame propagation speed could be affected in the Diesel engine and the boiler combustor by EGR. In terms of the flame spread rate and the transient temperature profile, numerical results have the qualitative agreement with the experiment.