Heat can be converted to electricity by thermoelectric generators (TEGs) directly. In consideration that the thermoelectric properties of the legs depend on the temperature strongly, the Thomson effect affects heat production, heat transfer, and energy conversion. Consequently, the Thomson effect cannot be neglected during evaluating the performance of the TEGs. In this work, we studied the influence of Thomson effect on the performance of the TEGs. Linear and polynomial fitting Seebeck coefficients of the thermoelectric materials are adopted and the three-dimensional thermo-electric coupled equations are solved by the finite-element method to obtain the output power and the conversion efficiency. Our results showed that the performance of the TEGs can either be depressed or promoted by the Thomson effect, depending on the temperature difference between the cold- and hot-ends and the Seebeck coefficient of the legs. Moreover, the Thomson effect always weaken the improvement of TEG performance by the means of increasing the figure of merit (ZT) of the thermoelectric materials. We then applied our model to study the performance of TEGs with Bi2Te3 as the legs and found the difference between the conversion efficiencies with Thomson effect and without Thomson effect increases fast with the temperature difference between the hot- and cold-ends. This study could be useful for guiding the searching for TEG system that are potentially high performance and compatible with environmental friendly application. (C) 2019 Elsevier Ltd. All rights reserved.