Energy analysis was applied to evaluate three typical straw-based power generation systems: 1MW gasification and power generation system, 5.5MW gasification and power generation system, and 25MW combustion and power generation system. Based on the concepts of energy costs and energy benefits, two indicators were employed: environmental yield ratio (EYR) and net energy. The results show that the 5.5MW system is the most efficient one in recovering energy from straw (the highest EYR) and is capable of saving the greatest quantity of energy per MJ of straw used (the highest net energy); the 1MW system is the best one in terms of energy costs, but the worst in terms of energy benefits. Compared with the 1MW system, the 25MW system has a lower EYR but higher net energy.