In order to determine the effect of the channel height to flame properties, drop tower experiments, numerical simulation and theoretical analysis methods are used to study flame propagation properties over thin solid fuels in different height channels under the microgravity condition. The height of the drop tower microgravity experiments is 10, 14 and 60 mm. The short time microgravity experiment results in 10, 14 and 60 mm channel heights indicate that flame spread rates increase with the increase of channel heights under same flow velocities. The flame lengths ratio of 10 and 14 mm channel heights is proportional to square of half channel height ratio. The results of numerical simulation and theoretical analysis show that flame spread rates and flame lengths are nonlinearly change with the increase of channel heights increase firstly, and then decreased. The heat release rate increased firstly and then decreased with the increase of channel heights, thus inducing to the nonlinear trend occurred in flame spread rate.