Thermoelectric generators are usually designed and optimized by finite element analysis. For accurate analysis, it is significant to establish a real-sized three-dimensional model of thermoelectric generator under actual application situations. In this paper, a real-sized three-dimensional finite element model of the thermoelectric generator is established and discussed. The height, cross-sectional area, and amount of thermoelectric pairs are alterable and programmable. The thermal input power is constant and the load resistance matches the internal resistance. The average temperature difference, the hot-side temperature distribution, and the output performance of the thermoelectric generator are calculated and discussed. Results indicate that changing the geometry or amount of thermoelectric pairs can influence the average temperature difference and hot-side temperature distribution simultaneously. However, changing the geometry or amount of thermoelectric pairs can only enhance the output voltage or current solely rather than simultaneously. (C) 2015 Elsevier Ltd. All rights reserved.