Abstract: In the face of the increasingly urgent need for the reduction of carbon emission and energy consumption, the development of efficient advanced thermal cycles with low carbon emission is becoming more and more important. A natural gas fueled semi-closed supercritical CO₂ cycle was proposed with zero carbon emission, and the semi-closed cycle was split into an open cycle and a closed cycle through working fluid splitting to further clarify the thermal to power conversion process. Furthermore, the cycle splitting method was applied to the complex modified cycle, which was split into several simple cycles to formulate the thermodynamic evaluation models of the different process modification measures and intuitively reveal the energy-saving mechanism of different cycle configurations. Through parameter sensitivity analysis, the optimum parameters of process modification measures were obtained. Results show that the cycle efficiency can be effectively improved by various cycle layout modification measures such as reheating, recompression, intermediate cooling and partial cooling, which can contribute to the efficiency improvement of 1.79~5.59 percentage points. After the integration and optimization of various process modification measures, the net power generation efficiency of the system is increased by 10.18 percentage points compared with the basic cycle.