A test bed for thermoelectric generator （TEG） was established to measure and improve the performance of a TEG. Through the experiment and corresponding analysis of computational fluid dynamics （CFD）， three different optimizing directions for the fluid field in the TEG were determined. The effects of these three directions：different numbers and heights of fin， different front and rear end heights of fin as well as different port lengths on the fluid field which eventually affects the performance of the TEG were analyzed using the ANSYS Fluent program. Finally a relatively optimal plan for the TEG was made on the basis of the hot end mean temperature and the uniformity of temperature distribution. The TEG was then modified and tested. The test result shows that under the testing conditions， the mean temperature difference between the cold and hot ends is increased by 8.8% and the electric power output by 5.8%.