To obtain a better view on flame speed at high temperature, laminar flame speeds of hydrogen/air, methane/air, ethene/air at different initial temperature, pressure and equivalence ratio were computed and analyzed, and turbulent flame speeds were given at different fluctuating velocity according to empirical model. The results show that laminar flame speed increases while increasing initial temperature or decreasing initial pressure for lightweight carbon-hydrogen fuel, and turbulent flame speed can approach hundreds of meters per second with high velocity fluctuation.