Abstract: A multi-physical field model of the solar reactor was established for a two-step thermochemical cycle of methane-reducing cerium oxide and water splitting. Model accuracy was verified by comparison with the experimental results. The coupling mechanism between various fields and its effect on improving the efficiency of solar fuel conversion were studied,and a cooperative optimization method among photothermal-chemical processes in the solar reactor was proposed. Results show that the temperature fluctuates due to the interaction between methane oxidation heat release and cerium oxide reduction heat absorption. Parameter sensitivity analysis shows that the yield of the reaction product can be improved with the increase of the reactor scale. The maximum solar-to-chemical efficiency can reach 38.75% under the condition of the optimal power and composition flow rate. This paper can provide a theoretical reference for the study of solar reactor mechanisms and amplification.