Encouraged by recent advances in solar-chemical fuel production, a moderately high-temperature solar thermochemical cycle based on GeO2/Ge is investigated thermodynamically. Since the GeO2/Ge redox has a great oxygen exchange capacity and suffers unfavorable phase change at high temperature, methanothermal reduction is Introduced to lower the operation temperature below melting point of redox. The calculated results indicate that reduction conditions of 875 K <= T-red <= 1200 K and CH4:GeO2 = 2:1 are conducive to achieving high selectivities of H(2 )and CO. As for the oxidation step, the H2O:Ge ratio of 8:1 is found abundant enough to ensure complete reoxidation of Ge. Isothermal and non-isothermal solar-to-fuel efficiency (eta(solar-fuel)) are compared, where R-oxi = 2 and R-oxi = 8 are suggested to pursue highest non-isothermal eta(solar-fuel) of 0.47 and isothermal eta(solar-fuel) of 0.28 respectively. In addition, the preferred site of CH4 adsorbing on GeO2 is predicted, and the calculated adsorption energy is lower than that of SnO2, indicating that GeO2 could be a suitable material for substrate before methanothermal reduction.