Abstract: In order to obtain acceptable cycle efficiency, current helium gas turbine power cycle technology needs high cycle temperature which means that the cycle needs high core-out temperature. The technology has high requirements on reactor structure and fuel elements materials, and also on turbine manufacture. While utilizing CO₂ as cycle working fluid, it can guarantee to lower the cycle temperature and turbo machine volume but achieve the same cycle efficiency, so as to enhance the safety and economy of reactor. According to the laws of thermodynamics, a calculation model of supercritical CO₂ power cycle was established to analyze the feature, and the decisive parameters of the cycle and also investigate the effect of each parameter on the cycle efficiency in detail were obtained. The results show that supercritical CO₂ power cycle can achieve quite satisfied efficiency at a lower cycle highest temperature than helium cycle, and CO₂ is a promising working fluid.