We established a three-dimensional finite element model of thermoelectric module based on low-temperature thermoelectric material bismuth telluride and medium-temperature thermoelectric material filled-skutterudite. The material properties of the thermoelectric materials such as the Seebeck coefficient, thermal conductivity, and electrical conductivity are temperature dependent. Based on the formal model, multi-stage models consist of low- and medium-temperature thermoelectric modules are proposed. The effect of input energy on performance of solar thermoelectric generator is considered according to the real operating condition. Results show that, reasonable thermal design of solar thermoelectric generator can take full advantage of the characteristics of thermoelectric materials and effectively improve the performance of power generation.