Abstract: This paper developed an optimal configuration method for an off-grid combined wind/PV-thermal energy supply system considering the natural carbon cycle. Firstly,we analyzed the influence of the uncertainty of wind and PV energy output on the reliability of the functional system and proposed the basic structure of the off-grid wind/PV-thermal combined energy supply system. Secondly,a natural carbon cycle model of functional systems is established based on the relationship between the maximum CO₂ absorbed by nature and the total energy demand of the world. Finally,we established a mathematical model for capacity optimal allocation of the power supply system,aiming at minimizing the total annual cost of the system,and solved it using a particle swarm optimization algorithm. The results of numerical experiments show that the proposed method achieves“net zero emission”of CO₂ in an off-grid wind/PV-thermal combined power supply system while ensuring the reliability of the power supply at a lower cost.