Hypersonic vehicle has become one of the research focuses because of its broad application prospects. The power supply issue in the long range/endurance of hypersonic propulsion system turns out to be one of the most important targets. Because the conventional power supply devices cannot meet the demands of a long range hypersonic air-breathing flight. In this work, a new scheme based on the expansion of high temperature cracked hydrocarbon fuel is proposed to solve the power generation problem. An analytical model for the expansion characteristics of the high temperature cracked hydrocarbon fuel is developed and validated by experiment data. The experimental results show that positive output work can be obtained with fuel working temperature even as low as 800 K and increases with fuel temperature. It also shows that the expansion work doing capability of cracked hydrocarbon fuel is much larger than the un-cracked fuel and greatly influenced by the fuel temperature, especially at the cracking temperature range. Especially, both experimental and calculation results show that the pressure also affects the high temperature thermal cracked hydrocarbon fuel expansion capability through influencing pyrolysis pathway of fuel and corresponding cracked components. The sensitivity analysis shows that the expansion work doing capability of fuel is more sensitive to the fuel temperature, especially at the hydrocarbon fuel pyrolysis starting and rapid increasing temperature region which is from 785 K to 855 K.